Mechanical imaging (MI) is a newly developed modality of medical diagnostics based on reconstruction of tissue structure and viscoelastic properties using mechanical sensors. The essence of MI is the solution to an inverse problem using the data of stress patterns on the surface of tissue compressed by a pressure sensor array. Imaged tissue structures are presented in terms of their viscoelastic properties. Evaluation of tissue 'hardness' (shear elasticity modulus) provides a means for characterizing the tissue, differentiating normal and diseased conditions and detecting tumors and other lesions. In contrast to the other existing methods of medical imaging which use sophisticated hardware such as superconductive magnets, expensive X-ray equipment and complex ultrasonic phased arrays, MI hardware consists of inexpensive mechanical sensors and a positioning system connected to a PC. A key feature of MI is 'knowledge-based imaging'. To produce a three-dimensional image, the computer uses both the measured parameters of an individual examined object and a general database on anatomy and pathology of the object. Two applications of MI are currently being developed: MI for mass screening and detection of breast cancer and MI for imaging the prostate and diagnosing prostate diseases. A prototype of the device for mechanical imaging of the prostate has been developed and is being tested clinically at the Robert Wood Johnson Medical School, New Jersey. The device is comprised of a transrectal probe with a position sensor and a pressure sensor array mounted on the articulated tip, an electronic unit and a PC. Results of extensive laboratory studies with rubber prostate models and initial data obtained in clinical trials strongly suggests that for certain applications the MI technology, as a new modality of imaging, has a diagnostic potential comparable to that of conventional diagnostic technologies. Mechanical imaging of the prostate appeared to be an efficient means of objectively evaluating and imaging the prostate and detecting prostate cancer.