The objectives of this study were to describe the knowledge of sexual and reproductive health among adolescents attending school and to compare the levels of knowledge between males and females and between older and younger groups of adolescents. Across-sectional study was conducted among 1,034 secondary school students using a self administered validated questionnaire. The items with the fewest correct responses included: whether one can get pregnant after a single act of sexual intercourse (30. 4%), whether sexual intercourse causes sexually transmitted diseases (STDs) (12.4%) and whether washing the vagina after sexual intercourse prevents pregnancy (17.0%). Their main source of sexual information was friends (64.4%). An independent t-test revealed the mean knowledge score was significantly higher among females than males on items assessing whether the genitalia may be touched freely by family members, females having attained menarche may become pregnant if having sex, whether pregnancy will occur if there is penetration of the penis into the vagina, whether premarital sexual intercourse causes pregnancy and if there is a relationship between abandoned babies and premarital pregnancies. The mean knowledge score assessing whether pregnancy can be prevented using condoms was higher among males than females. The mean knowledge scores were significantly higher among form four and form five students than forms one, two and three students. Lack of knowledge regarding important aspects of sexual and reproductive health warrant the need to strengthen sexual and reproductive health education.