Studies in varied settings have provided estimates of the prevalence of surrogate markers of benign prostatic hyperplasia (BPH). In population-based studies, the prevalence of moderate-to-severe lower urinary tract symptoms and depressed peak urinary flow rates increases across successively older age groups. Prostatic volume follows a similar pattern. Unlike clinic-based studies in which correlations are almost nonexistent, the population-based studies demonstrate a modest correlation among lower urinary tract symptoms, peak urinary flow rates, and prostatic volume. These cross-sectional observations extend to serum prostate-specific antigen levels and postvoid residual urine volumes. Data collected during the longitudinal follow-up study of men participating in the Olmsted County Study of Urinary Symptoms and Health Status Among Men provide a more detailed description of the natural history of changes in these surrogate markers of BPH. They also provide insights into their relation with each other and with long-term outcomes of BPH, such as acute urinary retention and treatment of BPH. These data demonstrate the progressive nature of BPH and are useful for the design and interpretation of clinical trials. Furthermore, they suggest that observational studies of etiology and prognosis should take advantage of the spectrum of disease reflected by the full range of values of these quantitative traits, rather than an arbitrary dichotomized outcome.