To evaluate the structural changes in the carpal tunnel and possible intrinsic median nerve damages in RA patients, quantitative bilateral magnetic resonance imaging (MRI) of the wrists was performed by means of a fast imaging sequence. Thirty-three women with RA and 42 controls were examined. The length of the carpal tunnel, the carpal tunnel volume/wrist volume (CTV/WV) ratio and the signal intensity of the nerve were calculated in both groups, bilaterally. The CTV/WV ratio was 0.12 in the patients and 0.11 in the control group (p = 0.007). A negative association was found between disease duration and carpal tunnel volume/wrist volume ratio (p = 0.049). Mean distal latency in the right motor median nerve was 3.0 +/- 0.4 msec (patients) and 3.4 +/- 0.6 msec (controls) (p = 0.002). Mean values in the right sensory branch were 1.2 +/- 0.1 msec (patients) and 1.4 +/- 0.3 (controls) (p = 0.01). The lack of association between the size of the carpal canal and neurophysiological parameters found in this study may suggest a possible protection of the median nerve by the increased canal size in patients with RA.