Despite the utility of penile plethysmography in helping diagnose sexual offenders, some men respond minimally to the test stimuli. This pilot investigation examined the effect of sildenafil on phallometric responding in a non-forensic sample (n = 12) of middle-aged males. Participants underwent phallometric testing on two separate occasions and were administered 50 mg of sildenafil prior to one of these sessions. Study data indicated that pre-treatment with sildenafil produced a significant mean percentage increase (28%) in peak response compared with the untreated condition. The implication of this result is discussed in view of the selected sample.