The existence and importance of patients with low penile buckling pressure and normal penile hemodynamic status have been recently recognized. We assessed the ratio of inadequate erection for vaginal penetration (low buckling pressure) in patients with normal penile vascular system proved with penile Doppler ultrasonography. A total of 101 patients with normal penile vascular status were retrospectively scrutinized dependent on penile axial rigidity (buckling pressure). Ninety patients had sufficient penile axial rigidity (> or = 550 g) whereas in the remaining 11 patients (11%) inadequate penile buckling pressure for vaginal penetration (< 550 g) was determined. Penile geometric and mechanical properties should not be overlooked during the evaluation of penile vascular system lest the patient be incorrectly diagnosed as having psychogenic impotence.