This study was designed to determine effects of peer-health-education on sexual health knowledge and attitudes of tertiary institution students in Imo State Nigeria by determining the mean gain scores of sexual health knowledge and attitudes after peer health education. Quasi-experimental (pre-test-post-test) research design was employed. Two hundred students drawn from the University, Polytechnic and College of Education, using a multi-stage sampling technique participated in the peer sessions which were facilitated by trained peer educators. Data were analyzed using ANCOVA and Z-test. (...) Findings revealed improved knowledge and attitudes on sexual health, as depicted by positive mean gain scores. Age group 16 - 20 years had the highest mean gain score ( X = 22.31) of sexual health knowledge than the rest, while age group 26 - 30 years had the highest mean gain score ( X = 10.59) of sexual health attitudes. Males had higher mean gain score ( X = 26.05) of sexual health knowledge, while females had higher mean gain score ( X = 9.77) of sexual health attitudes. The first years (100 level students) had the highest mean gain score ( X = 25.71) of sexual health knowledge and also had the highest mean gain score ( X = 14.12) of sexual health attitudes. Level of study was significant both for knowledge and attitudes (P < 0.01). It is recommended that peer-health-education be explored further as a method of communicating sexual health issues to tertiary institution students and youths generally. (shrink)