With the success of VTK (visualization ToolKit) and ITK (insight segmentation and registration ToolKit), there are more attentions to the toolkit development issue in medical imaging community. This paper introduces MITK (medical imaging ToolKit), an integrated 3D medical image processing and analyzing toolkit. Its main purpose is to provide a consistent framework to combine the function of medical image segmentation, registration and visualization. The design goals, overall framework, and implementation of some key technologies are provided in details, and some application examples are also given to demonstrate the ability of MITK. We hope that MITK will become another available choice for the medical imaging community.