Chlamydia trachomatis (C. trachomatis) is a major pathogen causing nongonococcal urethritis in men, together with Ureaplasma urealyticum and Mycoplasma genitalium [1]. There is little information about the prevalence of C. trachomatis genital infection in men in Croatia [2]. We sought to determine the prevalence of the C. trachomatis genital infection in symptomatic and asymptomatic men presenting for diagnosis at a public health laboratory, and to explore a possible association between patient age and C. trachomatis infection. . Patients (n = 888) were referred for a C. trachomatis test by their general practitioners. During the clinical examination, samples for C. trachmatis identification were collected and patients asked about the reason of their visit. Patients were divided according to their symptoms into following groups:1. Symptomatic patients (S): those showing urethral discharge and/or dysuria (n = 173). 2. Asymptomatic patients (A): those not showing any kind of symptoms (n = 280). This group comprised two subgroups: A 1 -patients undergoing the test as part of an extended periodical general medical examination (n = 129), and A 2 -patients whose sexual partners had certain non-specific urogenital complaints (n = 151).We excluded patients who came for a control examination after receiving a specific antimicrobial therapy (n = 158) and patients contacting a physician for untypical symptoms (lower abdominal or inguinal pain, arthritis of unknown cause, infertility problems) (n = 277) from analysis.Urethral swabs were collected using the specimen collection kit provided by enzyme immunoassay (EIA) manufacturer (MicroTak II Chlamydia EIA-Trinity Biotech). To detect the chlamydial antigen all urethral swabs were tested using EIA according to the directions on the package insert. In all specimens giving results above the cut-off value (presumptive positive results) confirmation was by direct fluorescent-antibody test.The ages of symptomatic and asymptomatic patients were compared using t-test for the independent samples in which equality of variances is not assumed (checked with Levene's test for equality of variance). The chi 2 -test was used to compare the prevalence of C. trachomatis infection in different age groups.Patients ranged from 18 to 79 years of age (average 34.63; SD = 11.31). There was no age difference between symptomatic and asymptomatic patients (t = 1.663; df = 451; p = 0.097). In symptomatic patients, the prevalence of C. trachomatis infection was higher (18.5%; CI 12.7-24.3) than in asymptomatic patients 80