A single blinded, quantifiable survey of prostate size in spinal cord injury (SCI) patients. A small prostate gland is sometimes found on routine digital rectal examination (DRE) in SCI patients. Interruption of neurohormonal supply to the prostate gland might lead to atrophy. To test this interpretation, transrectal ultrasonic (TRUS) examinations have been carried out in SCI patients stratified by severity of paralysis. Nine severely paralyzed spinal cord-injured men (levels at T10 or above and ASIA A, B, or C) were compared with 12 less severely paralyzed men (levels lower than T10 at any grade or ASIA D at any level). The groups were age matched. All patients were examined with a 90 degrees sector TRUS probe that measured the prostate gland in three dimensions and calculated the prostate volume and weight. Prostate-specific antigen (PSA) levels were also measured. By TRUS the prostate size was smaller in the severely paralyzed (range 8-16 g, mean 13 g) than in the less severely paralyzed (range 10-70 g, mean 28 g), P=0.02. The PSA level of the severely paralyzed group tended to be lower (0.5-2.1, mean 0.7 ng/ml versus 0.5-10.4, mean 2.2 ng/ml), P=0.08. The prostate gland of severely paralyzed SCI patients is small. Interruption of neurohormonal pathways due to extensive cord damage may be a factor.