OBJECTIVE: To evaluate the feasibility and efficacy of population-based outreach strategies to improve genital Chlamydia trachomatis (CT) screening in men. STUDY DESIGN: In a randomized trial, male enrollees ages 21-25 (n = 8820) were selected from the automated files of Group Health Cooperative and randomized to: a letter + test-request card for a CT urine home sampling kit (arm 1, n = 2940); a letter + mail-back sampling kit (arm 2, n = 2940); or a usual care control (arm 3, n = 2940). One reminder was sent to arms 1 and 2. The outcome was CT testing rates in the 4 months postrandomization. RESULTS: 105 of 2940 (3.6%) men in arm 1 and 230 of 2940 (7.8%) in arm 2 returned mailed specimens. All 335 respondents were sexually experienced, 43% had >2 sex partners in the past year, and 80% reported no genitourinary symptoms. Compared to arm 3, the relative risk of being tested was 5.6 (95% confidence interval (CI) 3.6-8.7) for arm 1 and 11.1 (95% CI 7.3-16.9) for arm 2. Arm 2 was significantly more likely to be tested than arm 1. CT prevalence for mailed-back specimens was 1.0% (1 of 105) for arm 1 and 2.6% (6 of 230) for arm 2; 70% of all positive intervention tests were from mailed samples. CONCLUSIONS: Both strategies resulted in significantly higher CT testing than usual care, but the intervention response rate was low (5.7% overall). Direct kit mailing performed best. In US populations, the value of mailed outreach strategies to men must be considered in the context of other CT screening priorities. © Copyright 2007 American Sexually Transmitted Diseases Association.