I have been using Colby Dillion's C# DICOM library mdcm for a while. This library provides all the DICOM functionality I have had the need for, but it has only been available for desktop applications until now.
However, I have started exploring whether the mdcm library can be sufficiently migrated to Silverlight. My continuous efforts can be followed here. At this stage I have made all shortcuts necessary to make the Silverlight class library build at all, and I have only included the most central parts of the original library. In due time I will fine tune the shortcuts to mimic the original library as much as possible, and I will try to add as many missing parts as I can.
It will be exciting to see if this effort can eventually result in a true open source alternative for DICOM functionality in Silverlight!