Magnetic resonance (MR) imaging of the carpal tunnel was performed in 23 wrists of 13 patients who were suspected to have carpal tunnel syndrome (CTS). In ten out of 23 wrists, diagnostic images of the carpal tunnel could be obtained. MR images were analysed retrospectively as to swelling of the median nerve, signal intensity of the median nerve on T2 weighted image, and swelling of the tendon sheath. In 8 wrists the median nerve was significantly swollen at the inlet of the carpal tunnel. Four of them showed increased signal intensity of the median nerve on T2 weighed image at the inlet. Swelling of the tendon sheath was demonstrated in two cases. These finding seem to represent edematous change of the median nerve due to compression. Surgical correlation was obtained in two wrists. Since MR imaging is capable of demonstrating pathological changes of the median nerve in CTS, it can be a diagnostic tool in selected cases.