Computer aided diagnosis (CAD) is a currently applied computerized analysis of medical images and is widely used as a tool in detection and differential diagnosis of abnormalities in medical imaging. In clinical practice CAD became a very useful implement in various imaging techniques such as mammography, radiography, CT, MRI or diagnostic ultrasound. CAD became also a major research subject in clinical radiology e.g. in detection of pulmonary nodules in chest CT or breast cancer on mammograms. CAD concept, unlike known from 1960s automated computer diagnosis concept (ACD), which is based on computer algorithms only takes into account equally the roles of physician and computer. Current directions in CAD development focus on continuous improvement of overall performance in detection of pathological lesions and assembling CAD schemes as packages implemented as a part of PACS system. The aim of this article is presentation of the concept of computer aided diagnosis, current opportunities of adopting CAD systems into various imaging techniques and new directions in CAD development.