Horos

Horos is a free, open-source DICOM viewer for macOS, used by dentists, radiologists, surgeons, researchers and students who work on a Mac. It is a community fork of OsiriX, released under the GNU LGPL 3.0, and Purview is the project’s chief sponsor.

If you are looking for the Horos DICOM viewer for Windows, there isn’t one. The Horos project states that it runs only on Mac computers (macOS 10.11 or later). Windows users need a different viewer; see the alternatives below. On a Mac, Horos is one of the most capable free ways to review CBCT, CT and X-ray studies.

Horos at a glance

What it does

• Local DICOM database: import studies from folders, discs and USB drives, then search and sort by patient and date.
• 2D viewing with window/level, zoom, pan and ROI tools for length, angle and area.
• Orthogonal and oblique multiplanar reconstruction (MPR) of CT and CBCT volumes.
• Curved MPR (CPR): trace a path and get straightened and stretched reformations with transverse cross-sections.
• 3D volume rendering and surface rendering.
• Export of rendered surfaces to STL, OBJ or VRML files.
• PACS query/retrieve and sending studies to other DICOM nodes.
• Burning studies to CD/DVD, and a plug-in system (including the HorosCloud plug-in for Purview’s optional paid sharing and reporting service).

How dental teams use it

Reviewing a CBCT scan on a Mac

1. Copy the DICOM folder from the disc or USB stick to the Mac.
2. Drag the folder into the Horos database window, or use the import command, and wait for the study to appear.
3. Open the series in the 2D viewer and adjust window/level so bone and teeth are clear.
4. Open 3D MPR to align axial, coronal and sagittal planes with the area of interest.

Building a panoramic-style view with curved MPR

1. Open the CBCT series in the curved MPR (CPR) viewer.
2. Place points along the centre of the dental arch on an axial slice.
3. Horos produces a straightened reformation that reads like a panoramic image, plus cross-sections perpendicular to the path.
4. Step through the cross-sections to assess bone width and height, and measure with the length tool.

Exporting a 3D surface for a model or presentation

1. Open the volume in surface rendering and set a threshold that separates bone or teeth from soft tissue.
2. Export the surface as STL (OBJ and VRML are also available).
3. Clean the mesh in MeshLab or Blender before printing. CBCT grey values are not calibrated like medical CT, so choose the threshold by eye and check the result.

Install and first run

• Choose the right build: the Apple Silicon build (4.0.1) for M-series Macs, the Intel build for older Macs. The project promotes 4.0.1 for Apple Silicon and macOS 26 Tahoe.
• Install: open the DMG, drag Horos to Applications and start it. If macOS asks for confirmation on first launch, approve it in System Settings, Privacy & Security.
• Hardware: any Mac that runs macOS 10.11 or later can start Horos. The project recommends at least an i5 processor, 16 GB RAM and a discrete GPU or Intel Iris graphics for comfortable 3D work.
• Do not keep the database in iCloud. The Horos FAQ warns that syncing it between Macs with the same Apple ID can corrupt the database or overwrite images.
• Crash at start: the official troubleshooting is to replace the HorosCloud plug-in, either via Plugins, Manage Plugins, or by swapping the plug-in file in the user Library folder.

Limitations

• macOS only. No Windows, Linux, iPad or iPhone version of Horos itself.
• Horos does not claim FDA clearance or CE marking. Treat it as a review, teaching and research tool, and follow your local rules for primary diagnosis.
• Releases are infrequent. The current Apple Silicon installer dates from 2023, although the source code received macOS 26 build fixes in 2026.
• No dental-specific tools such as implant libraries, surgical guides or tooth charting.
• Help comes from the community; the detailed user guide, training and direct support are paid services from Purview.

Horos vs alternatives

Weasis is also free and open source, runs on Windows, macOS and Linux, and has a curved MPR designed for tracing the dental arch on CBCT. It is the natural choice if your team mixes Macs and PCs. RadiAnt DICOM Viewer is a fast Windows viewer with MPR, 3D and STL export, but it is shareware (conditionally free) and not supported on macOS. OsiriX, the project Horos was forked from, is a commercial Mac product from Pixmeo. For segmentation of teeth and jaws, 3D Slicer goes much further than Horos.

FAQ

Is Horos free?

Yes. Horos is free and open source under the LGPL 3.0. The project asks for donations, but you do not have to donate to download or use it.

Is there Horos for Windows?

No. Horos runs only on macOS. On Windows, use Weasis (free) or RadiAnt DICOM Viewer (shareware).

Is there Horos for iPad or iPhone?

Horos is a desktop Mac application. The Horos site lists “Horos Mobile” as a trademark of iCat Solutions, which makes it a separate product.

Does Horos work on macOS Tahoe?

The project promotes Horos 4.0.1 for Apple Silicon and macOS 26 Tahoe. If an older build fails to start after upgrading macOS, install the current build for your processor.

Horos vs OsiriX: what is the difference?

Horos grew out of the open-source OsiriX code base and is free under the LGPL. OsiriX is Pixmeo’s commercial product.

Horos vs Weasis: which should I choose?

On a Mac-only team, either works. Weasis wins when you also need Windows or Linux, while Horos offers STL export of 3D surfaces.

How do I use Horos?

Import the DICOM folder into the database, open the series in the 2D viewer, then use the 2D/3D tools for MPR, curved MPR and rendering. Purview sells a detailed user guide and video training.

What is a Horos alternative for Windows?

Weasis is the closest free alternative: open source, cross-platform and able to build panoramic views from CBCT.

Last checked against official sources: 26 September 2026 (developer website: horosproject.org). Versions and licence terms change — confirm on the developer's site before deploying in a clinic.