Early life sexual factors, including histories of sexually transmitted infections, young-onset prostatitis, and frequency of ejaculation, were investigated in relation to lower urinary tract symptoms (LUTS) in a large case-control study nested within the Health Professionals Follow-up Study. In 1992, study participants were asked to provide information on their histories of sexually transmitted infections, prostatitis, ejaculation frequency, surgery for an enlarged prostate, and LUTS. Information on prostate surgery and LUTS was updated every 2 years. LUTS cases were defined as men who reported surgery for an enlarged prostate or high-moderate to severe LUTS (> or = 15 points on the American Urological Association symptom index) on any study questionnaires (n = 4,608). Controls were men who did not report surgery for an enlarged prostate and who scored 0-7 points on the American Urological Association symptom index on all questionnaires (n = 17,967). History of gonorrhea (adjusted odds ratio = 1.76, 95% confidence interval: 1.43, 2.15) or young-onset prostatitis (adjusted OR = 1.55, 95% confidence interval: 1.22, 1.96) was positively associated with LUTS. No association was observed between ejaculation frequency in early adulthood and LUTS. These results suggest that early genitourinary infections may contribute to later development of LUTS, although confirmation in additional population settings is warranted.