Purpose: To determine the feasibility and affect of mass media use in a population-level intervention for chlamydia screening promotion. Methods: A population-level chlamydia intervention protocol was field tested. The intervention, targeting 15-25-year-old individuals, was designed to: (a) increase awareness of personal risk for chlamydial infection; (b) facilitate dissemination of chlamydia knowledge by use of a telephone hot line; and (c) promote care-seeking behavior (report for a chlamydia screening program). The intervention activities included: (a) mail outreach, (b) a television and radio campaign, (c) a prerecorded Check-It-Out chlamydia hot line, (d) a staffed chlamydia Options information line, and (e) a free confidential urine ligase chain reaction (LCR) test for chlamydia. Mass mailings were scheduled at intervals, starting two-weeks before the beginning of the television advertisement. The 30-second television advertisement was aired on local television stations 130 times in a 6-week period. The outcome measures were quantity and characteristics of incoming calls to the automated hot line and staffed chlamydia information phone line in response to the chlamydia campaign, and response to the urine screening program. Descriptive and bivariate analyses were used to evaluate the outcomes. Results: The hot line was called 642 times during the monitoring period (November 1, 1999 to March 8, 2000), the majority (92%) during the 6 weeks of television advertisement, with an average of 99 calls per week, compared with an average of 9 calls per week after the commercial ended. Each bulk mailing was accompanied by a boost in the incoming hot line calls. The research staff triaged 133 calls to the "Options" phone line, 81% in the 6 weeks of the TV ad. The mean age of the 133 callers was 23.9 ± 7.7 years (range 14-49 years). A majority called for screening information; 67% of callers were females and 84% of female callers were under age 26 years. Five percent of callers identified themselves as a parent of a teenager. The majority credited the TV ad as their source of the hot line number. Thirty-one individuals reported for a confidential chlamydia screening, 27 of 31 (87%) during the 6 weeks of TV advertising. No negative responses regarding the chlamydia campaign were encountered. Conclusion: This report describes strategies used to implement and measure the effectiveness of a mass media campaign and demonstrates evidence that mass media is effective in delivering STD intervention messages to young people. © Society for Adolescent Medicine, 2002.