BACKGROUND: In Switzerland (population 7.4 million), 3 different systems contribute to surveillance for sexually transmitted infections. GOAL: The goal of this study was to compare time trends from surveillance systems for chlamydia, gonorrhea, and syphilis. STUDY DESIGN: We studied surveillance data (1997-2003) from laboratory reports in women and men, men attending dermatology clinics, and women attending gynecologists. RESULTS: Laboratory reports of episodes of Chlamydia trachomatis and Neisseria gonorrhoeae increased by 31% (from 2573 to 3449 cases) and 104% (from 259 to 528 cases), respectively. Over the same period, chlamydia reports from men attending dermatology clinics and women attending gynecologists did not change and dermatology clinic-based reports of gonorrhea in men increased only slightly. Syphilis reports from dermatology clinics increased by 127% (from 22 to 50 cases). CONCLUSIONS: Increases in laboratory reports of chlamydia and gonorrhea were not consistently detected in sentinel populations. Numbers of cases reported to all 3 systems were low. The performance of surveillance systems for sexually transmitted infections should be evaluated regularly.