The aim of this study is to find out the efficacy and safety of azithromycin in the treatment of males with uncomplicated non-gonococcal urethritis. It is an open, non-comparative study carried out in the major sexually transmitted disease clinics in Hong Kong. The subjects were 45 male outpatients with clinical symptoms and signs of acute non-gonococcal urethritis. Patients presenting with acute urethritis were examined and non-gonococcal urethritis were examined and non-gonococcal urethritis was daignosed by the positive urethral smear for white blood cells but negative for gonococcus. They were given a single 1 gram oral dose of azithromycin at the clinic. Follow-ups after one and two weeks to examine for cure and adverse events were made. The result showed that 35 out of 42 evaluable patients were cleared of urethritis. Only 2 out of 22 chlamydial antigen positive patients still remained positive at the last visit. Adverse events were not uncommon but all were only mild. We concluded that 1 gram single dose of azithromycin was effective and well tolerated in the treatment of non-gonococcal urethritis in male patients.