The treatment of impotence in diabetic men with vacuum tumescence therapy was studied in a specialist clinic. Of 54 diabetic men referred with impotence, seven declined treatment, three chose self-injection with papaverine, and 44 chose vacuum therapy. Patients underwent autonomic function testing (heart rate response to respiration), measurement of penile blood flow (duplex Doppler scanning), and estimation of serum prolactin and testosterone levels. After 2 months, 33 men (75%) were able to have satisfactory intercourse using vacuum therapy. Three others could produce a satisfactory erection with vacuum therapy but their partners found it unacceptable. Eight men (18%) were unable to have satisfactory intercourse; six of these were later treated by self-injection. The median frequency of use of vacuum therapy was 5.5 (1-26) times a month. Outcome was independent of penile blood flow, autonomic function or endocrine status. Impotent diabetic men should be given counselling and offered a choice of the available treatments. Vacuum tumescence therapy is an effective and simple treatment which requires little investigation.