This study examined some characteristics of male clinic attenders with urethral chlamydial infection. The prevalence of urethral chlamydial infection among heterosexual men (men who have sex with women [MSW]) was 446 (17%) of 2684 men. Men aged 16-34 years were more likely to have chlamydiae than older men with only casual partners (chi2 = 16.08; P = 0.001). Infected younger men with casual partners had more partners than uninfected men (median 2.0 [interquartile range [IQR] 1.0] versus 1.0 [IQR 1.0]) (P<0.05). However, this was not true of older men (median number of partners 1.0 [IQR 1.0] versus 1.0 [IQR 1.0]) (P>0.05). Consistent condom use by younger but not by older men was associated with a lower prevalence of chlamydial infection compared with those whose use of condoms was inconsistent (chi2 = 19.75; P<0.001). Our results suggest that chlamydia testing should be offered to any MSW, irrespective of his age, who has had a new partner.