Colonoscopy is important since cancer of the colon and of the rectum is the second most malignant tumor in industrialised countries. At present, however, colonoscopy is a procedure often painful for the patient and complex for the doctor. This is mainly due to the characteristics of the endoscopes currently used for colonoscopy, which are quite rigid and require the doctor to exert forces and rotations at the shaft for insertion. In this paper we present the concept and describe the design and fabrication of a new system for colonoscopy based on a microrobot capable of propelling semi-autonomously along the colon. The microrobot system comprises a mothership incorporating devices for clamping the colon wall and tools for diagnosis and intervention; an actuation system based on Shape Memory Alloy (SMA) pneumatic microvalves; and a Human/Machine Interface allowing the doctor for teleoperating or supervising the functioning of the microrobot and for receiving visual and other information during endoscopy. A prototype microrobot system has been tested in vitro with promising results. 6 Developed by a multidisciplinary team of engineers and medical doctors the proposed microrobot system has the potential for further miniaturisation'and functional integration of instrumentation and tools for intracavitary diagnosis, therapy and surgery, thus representing an attractive opportunity for a wide range of new applications in minimally invasive surgery and therapy.