['To investigate the anomalous rises in maximum urinary flow rates seen in a prostate-diagnostic clinic.', 'The study comprised 1994 men aged 40-79 years registered at five health centres in Central Scotland, participating in a study of the natural history of benign prostatic hyperplasia (BPH), who completed a urodynamic assessment on up to three occasions: in the community, on referral to a prostate-diagnostic clinic and at a one-year follow-up.', 'Subjects referred to the diagnostic clinic on the basis of maximum flow rate (Qmax < 15 mL/s) and/or urinary symptomatology showed a mean increase in Qmax (P < 0.001) when tested at the clinic and at the one-year follow-up. In health centres which referred men to the clinic with no pre-selection, there were no significant changes in Qmax.'] Does regression to the mean occur in measuring peak urinary flow?