Background: Health-seeking and sexual behaviors are important elements in the control of sexually transmitted infections (STIs). Goal: To examine patterns of health-seeking behavior and related sexual behavior relevant to improved prevention and care among patients attending primary healthcare (PHC) clinics. Study Design: A questionnaire covering social, demographic, and healthcare-seeking and sexual behavior information was administered to 555 patients attending three primary healthcare clinics in low socioeconomic areas of Nairobi, Kenya. Results: Women's knowledge about health in general and STIs in particular was poor. A major gender difference in delay of health seeking for STIs was observed (5 days for men versus 14 days for women). Significantly more men than women reported a history of STIs (68% versus 47%; P = 0.04). Men reported more extramarital affairs (17% versus 8%; P < 0.001). A high prevalence of gonorrhea (3%) and chlamydia (6%) was found in this population, with no difference between the genders. The urine dipstick was ineffective for the detection of these STIs. Conclusions: There is a need for better understanding of behavioral factors, as well as gender and social aspects of health care. Health education and health promotion in these areas should be strengthened. Improved screening tests are needed for the detection of STI.