Objectives: To estimate the prevalence of chlamydia infection in young men in the Mid-Western Health Board Region of Ireland, and to determine risk factors for its acquisition. Methods: Consecutive men attending orthopaedic clinics (OPD), and a university sports arena (UL) were recruited to a chlamydia prevalence study. All men aged 17-35 who had been sexually active and had not passed urine in the last hour were eligible. Information about chlamydia was given, informed consent obtained, and a self administered questionnaire was completed. A first void urine (FVU) was collected and tested by ligase chain reaction (LCR). Results: 82% (207/252) of men from OPD, and 60% (186/310) from UL participated. 6.3% (13/207) from the OPD and 5.4% (10/186) from UL tested LCR positive, giving an overall prevalence of 5.9% (23/ 393). Proved risk factors for chlamydial positivity were: (1) more than one sexual partner in previous 6 months, (2) more than eight lifetime sexual partners, (3) current symptoms (dysuria or discharge). No statistical significance was found for age, condom use, smoking, days since last sexual intercourse and previous GUM clinic attendance. No statistically significant difference to cost effective prevalence of 6% was shown. Conclusions: A 5.9% prevalence of Chlamydia trachomatis was found which is cost effective to screen and treat. Non-invasive screening of men in the community was possible. Numbers of sexual partners and current symptoms were significant risk factors. Since only 25% of men in this laboratory were diagnosed with chlamydia outside the GUM clinic, compared with 59% of women, it is important that community screening of men is promoted.H ealthcare providers often see chlamydial infection, like other STDs, as a women's health issue, as its complications in women are well known. As a result, men are relatively ignorant about its transmission, prevention, and control.1 No doubt this is partially because 50%-70% of infections in women 2 and 40%-50% of those in men 3 are clinically silent. Research in the United States and Sweden has shown that detection and treatment of asymptomatic infections in women result in a reduction of complications. 5The number of diagnoses of chlamydia has been consistently higher in women than men, by more than 30%. 6 In the Limerick regional laboratory in the 12 months up to October 2003, almost twice as many women (264/3851) as men (149/ 1496) were diagnosed positive. Over 75% of chlamydia positive men (112/149) were patients in the GUM clinic, compared to 41% of women (109/264). Screening men for chlamydial infection, especially those without symptoms has been considered problematic, 1 mainly because men are less likely than women to attend healthcare settings. 7 In the past, screening asymptomatic men was further hampered by the necessity for invasive sampling techniques.