[Overview of computer-aided diagnosis]. 
Computer-aided diagnosis (CAD) systems have been developed in many institutions.  CAD is able assist radiologists and physicians in detecting lesions and in differentiating benign from malignant lesions on medical images.  The output from CAD can be used as a "second opinion" to assist radiologists in their interpretations and improve diagnostic accuracy.  It is important to note that CAD is not designed for the automated diagnostic system.  A few commercial CAD systems have recently been developed by venture companies, with pre-marketing approval having been obtained from the U.S. Food and Drug Administration (FDA).  It is clear that CAD has practical value in radiologic diagnosis.  In this paper, the background of CAD research and important topics, including the usage of an image database and methods of evaluating the performance of typical CAD schemes, are discussed.  The number of CAD researchers in Japan is not yet sufficient.  Radiological technologists who have a strong interest in CAD research will be good partners for radiologists in developing CAD schemes.