Common things are common perhaps because they reflect common pathophysiological principles. Non-gonococcal urethritis (NGU) is a common problem. In 1998 over 520 000 episodes of NGU were reported from genitourinary medicine clinics in England.¹ Systematic reviews on its pathogenesis and treatment are long overdue. In their absence it might be useful to list some of what we do know about the aetiology and associations of this common and enigmatic problem.

We know that 30–50% of men with NGU have a persistent inflammation,² and that even after a course of currently recommended antibiotic therapy the inflammatory stimulus remains for several weeks (months?) in the urethra after chlamydial and non-chlamydial NGU.³ We know that chlamydia is isolated from approximately half of patients presenting with their …