The aim of this study was to determine the incidence and characteristics of pain following intracavernous injection of prostaglandin E1 (PGE). We injected PGE into the cavernous tissues of 156 patients with erectile dysfunction who had never previously been injected with PGE. The incidence and characteristics of pain after injection were evaluated by the patients' response to a questionnaire. The intensity of pain was determined by the degree of impediment to intercourse, verbal rating scale (VRS), numerical rating scale (NRS), and visual analogue scale (VAS). Patients scoring 'no pain' on the VRS, NRS, and VAS were 11.5%, 7.7%, and 7.7%, respectively. Overall incidence of pain was 91%. There was 'much' or 'very much' impediment to intercourse because of pain in 14 (9.1%) patients. The most common kind of pain was 'heavy pain' in 90% of the patients followed by 'throbbing' in 38%, 'aching' in 21%, 'tightening' in 18%, and 'shooting' in 13%. The mean duration of pain was 101.2 +/- 63.7 minutes and it lasted during the entire erection period in 71(50.4%) patients. There were significant correlations among the degree of impediment to intercourse, VRS, NRS, and VAS scores (all p < 0.01). However, no association was noted between pain intensity and both erectile response to PGE and injected dose. The higher incidence of intracavernous PGE-induced pain reported here compared to other studies might be related to difference in pain thresholds among races. The high incidence of pain but low frequency of much impediment to intercourse would be related to the pain characteristics as well as the intensity of pain.