A case control study was conducted on 100 patients with benign prostatic hypertrophy (BPH) and 100 controls matched by age and residence. Interviews were performed by well-trained urologists using an original questionnaire. Matched-pair analysis revealed the following characteristics and relative risks (RR) as being significantly (P less than 0.05) different among the BPH patients versus the controls: higher educational background (RR = 2.77); not engaged in farming, forestry, or fishing (RR = 4.82); no environmental pollution at work (RR = 2.90); a present annual income of more than 2,400,000 yen (RR = 3.84); a previous annual income of more than 2,400,000 yen (RR = 3.82); practice the highest standard of living (RR = 4.24); more than two children (RR = 2.67); experienced first nocturnal emission before reaching the age of 20 (RR = 3.11); expanding more than 10 min to complete one act of sexual intercourse (RR = 2.43); having no episode of sexual impotence that lasted more than 1 month (RR = 2.29); no family history of gastric ulcer (RR = 7.98); no family history of breast cancer (RR = 8.25); regular consumption of milk (RR = 2.25); irregular consumption of green and yellow vegetables (RR = 3.91); and pickles not consumed at every meal (RR = 1.99). Characteristics that did not achieve a high level of statistical significance (0.05 less than P less than 0.10) between cases and controls were as follows: past history of gonorrhea, urethritis, or prostatitis and syphilis (RR = 1.84, 2.76, and 4.26, respectively), and daily meat consumption (RR = 3.18). On the basis of interviews of the patients and cases reported in this study, we conclude that dietary and sexual habits may be important factors which place individuals at a higher risk for developing BPH.