By continuous and simultaneous recording of nocturnal penile rigidity and circumferential expansion (tumescence), nocturnal penile rigidity and tumescence have been classified into 6 patterns: normal, dissociation, uncoupling, short episode, low amplitude and flat trace. The monitoring will be helpful to diagnose underlying disorders involving erectile impotence, if the pattern of nocturnal penile rigidity and tumescence are related with the disorders. This study analyzed the relationship between the pattern of nocturnal penile rigidity and tumescence and associated disorders in 105 patients with erectile impotence. Of 15 patients with central nervous system disorders, 9 (60%) had a pattern of short episode of rigidity. In 29 patients with cardiovascular disorders, the patterns of dissociation, low amplitude and flat trace were the main findings and observed in 41, 41, 35% of the group, respectively. No patients with diabetes mellitus showed normal pattern. Although the group of non insulin dependent diabetes mellitus (21 patients) had various patterns of rigidity and tumescence, the insulin dependent group (14 patients) mainly showed patterns of low amplitude (21%) and/or flat trace (71%). The continuous and simultaneous monitoring of penile rigidity and tumescence will be helpful, with an integral analysis of its pattern and other examinations, for accurate diagnosis of underlying disorders of organic impotence, besides for differentiation of organic impotence from psychogenic one.