To characterise the progression and treatment of lower urinary tract symptoms (LUTS) among men aged 45-69 years in the California Men’s Health Study. A total of 39,222 men, aged 45-69 years, enrolled in the Southern California Kaiser Permanente Health Plan were surveyed in 2002-2003 and again in 2006-2007. Those men who completed both surveys who did not have a diagnosis of benign prostatic hyperplasia (BPH) and were not on medication for LUTS at baseline were included in the study (N = 19,505). Among the men with no or mild symptoms at baseline, the incidence of moderate/severe LUTS (American Urological Association Symptom Index [AUASI] score ?8) and odds of progression to severe LUTS (AUASI score ?20) was estimated during 4 years of follow-up. Of the 9640 men who reported no/mild LUTS at baseline, 3993 (41%) reported moderate/severe symptoms at follow-up and experienced a 4-point change in AUASI score on average. Of these men, 351 (8.8%) had received a pharmacological treatment, eight (0.2%) had undergone a minimally invasive or surgical procedure and 3634 (91.0%) had no treatment recorded. Men who progressed to severe symptoms (AUASI score ?20; n = 165) were more likely to be on medication for BPH (odds ratio [OR] 8.09, 95% confidence interval [CI] 5.77-11.35), have a BPH diagnosis (OR 4.74, 95% CI 3.40-6.61) or have seen a urologist (OR 2.49, 95% CI 1.81-3.43) when compared with men who did not progress to severe symptoms (AUASI score <20). These data show that the majority of men who experienced progression did not have pharmacological or surgical therapy for their symptoms and, therefore, may prove to be good candidates for a self-management plan.