How to Open DICOM Files (Online, Windows & Mac)
DICOM (.dcm) is the standard file format for medical images such as CT, MRI, X-ray and ultrasound studies. Regular photo apps cannot open it — but you have three easy options, and the fastest one needs no installation at all.
Option 1: Open DICOM files online (no install, no upload)
- Open the free online DICOM viewer in any modern browser.
- Drag and drop your DICOM files — or the whole study folder — onto the viewer. You can also click Open DICOM Files and select them manually.
- Your series appear in the left panel with thumbnails. Click one to review it: scroll through slices with the mouse wheel, adjust brightness/contrast, zoom, measure and more.
Everything happens locally in your browser. The files are never uploaded to a server, which matters because DICOM files usually contain patient information.
No account, no upload, no installation — works on Windows, Mac and Linux.
Open DICOM Files NowOption 2: Free desktop viewers for Windows
- MicroDicom — lightweight free viewer for everyday use.
- RadiAnt DICOM Viewer — polished commercial viewer with a free trial.
Desktop viewers make sense if you review large studies every day or need advanced diagnostic tooling. For occasionally opening a CD or a few files, the browser route is quicker.
Option 3: Free desktop viewers for Mac
- Horos — free, open-source viewer for macOS.
- OsiriX Lite — free edition of the well-known OsiriX workstation.
My file has no extension — is it still DICOM?
Very often, yes. Files exported from scanners or hospital CDs frequently have no
extension, or use .ima instead of .dcm. A DICOM file starts with
a 128-byte header followed by the letters DICM. You do not need to rename
anything: just drag the files (or the folder that contains them) into the
online viewer — it detects DICOM content regardless of the extension.