Nocturnal penile tumescence and rigidity testing (NPTR) has traditionally been performed to distinguish psychogenic from organic impotence. However, considerable lack of uniformly accepted normative data for NPTR readings makes the reproducibility of the method questionable. In this study, we try to evaluate the impact of aging as independent criteria for quality of erectile episodes. A total of 455 patients (ages 20-71 y) whose initial complaints were erectile dysfunction underwent two nights NPTR measurement with Rigiscan device. After analyzing the data, 353 men out of 455 were regarded as having normal NPTR recordings. The number of normal erectile episodes (erectile episode of penile tip rigidity greater than 60% more than 10 min duration), RAU Tip, RAU Base, TAU Tip, TAU Base, Average event rigidity of Tip (%), Average event rigidity of Base (%) and Duration of erectile episodes > or =60% minute were re-evaluated with regard to five age groups (group I: <30 y; group II: 30-39 y; group III: 40-49 y; group IV: 50-59 y; group V: > or =60 y). The mean values of erectile episodes in the age groups were as follows: group I, 2.46; group II, 2.28; group III, 2.40; group IV, 1.58; group V, 1.27. When we analyzed the groups between themselves, we observed statistically significant difference after the age of 50 y. The mean erectile episodes in patients younger than 50 y were 2.37 (s.d.: 1.50), whereas 1.49 (s.d.: 1.15) in patients older than 50 y (P<0.001). We also observed statistically significant difference at all of the above-mentioned NPTR parameters with regard to age. The results of our study showed that aging negatively influence quality of nocturnal erections especially after 50 y and we suggest that age needs to be taken into account in the diagnostic interpretation of NPTR testing.