To examine whether a history of sexually transmitted infections (STIs) or positive STI serology is associated with prevalent and incident benign prostatic hyperplasia (BPH)/lower urinary tract symptoms (LUTS)-related outcomes in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial.Self-reported history of STIs (gonorrhoea, syphilis) was ascertained at baseline, and serological evidence of STIs (Chlamydia trachomatis, Trichomonas vaginalis, human papillomavirus (HPV)-16, HPV-18, herpes simplex virus type 2, human herpesvirus type 8 and cytomegalovirus) was detected in baseline serum specimens. We used data collected on the baseline questionnaire, as well as results from the baseline prostate-specific antigen (PSA) test and digital rectal examination (DRE), to define prevalent BPH/LUTS-related outcomes as evidence of LUTS (self-reported diagnosis of an enlarged prostate/BPH, BPH surgery or nocturia [waking ≥2 times/night to urinate]) and evidence of prostate enlargement (PSA > 1.4 ng/mL or prostate volume ≥30 mL) in men without prostate cancer. We created a similar definition of incident BPH using data from the follow-up questionnaire completed 5-13 years after enrolment (self-reported diagnosis of an enlarged prostate/BPH or nocturia), data on finasteride use during follow-up, and results from the follow-up PSA tests and DREs. We used Poisson regression with robust variance estimation to calculate prevalence ratios (PRs) in our cross-sectional analysis of self-reported (n = 32 900) and serologically detected STIs (n = 1 143) with prevalent BPH/LUTS, and risk ratios in our prospective analysis of self-reported STIs with incident BPH/LUTS (n = 5 226).Generally null results were observed for associations of a self-reported history of STIs and positive STI serologies with prevalent and incident BPH/LUTS-related outcomes, with the possible exception of T. vaginalis infection. This STI was positively associated with prevalent nocturia (PR 1.36, 95% confidence interval (CI) 1.18-1.65), prevalent large prostate volume (PR 1.21 95% CI 1.02-1.43), and any prevalent BPH/LUTS (PR 1.32 95% CI 1.09-1.61); too few men had information on both STI serologies and incident BPH/LUTS to investigate the associations between T. vaginalis infection and incident BPH/LUTS-related outcomes.Our findings do not support associations of several known STIs with BPH/LUTS-related outcomes, although T. vaginalis infection may warrant further study.