A procedure for automatic deletion of extracranial parts and bone in computed tomography (CT) pictures is presented. Such a procedure is a prerequisite for many types of quantitative image analysis. The algorithm can delineate complex bone contours and is completely independent of information outside the skull. Special options allow, in addition, the deletion of calcified parts of the brain and of some artifacts. The program is implemented in a general program system (PICPRO) developed for CT image analysis and picture manipulation.