Previous sex education research has neglected to examine systematically the effects of different types of instruction formats. In the present study, 193 undergraduates were assigned to one of the following conditions: (1) lecture only; (2) small group discussion only; (3) lecture + small group discussion; (4) lecture + extra lecture/review; and (5) no intervention control. Pre- and posttest measures assessed the dimensions of sexual guilt, sexual attitudes, and sexual anxiety. Results revealed significantly greater reductions in sexual guilt for the lecture only, lecture + small group discussion, and lecture + extra lecture/review conditions than for the no intervention control condition. Significantly greater changes in the direction of more tolerant sexual attitudes were found for the small group discussion only and lecture + extra lecture/review conditions than for the no intervention control condition. No other significant results were found. Contrary to expectation, the addition of 9 hours of small group discussion to a semester-long lecture format course did not result in significantly greater positive changes on the dimensions assessed than those achieved by lecture alone. The implications of these findings for the design of sex education courses are discussed. Recommendations for future research include assessment of the long-term effects of sex education on dimensions such as quality of sexual adjustment and consistency of contraceptive usage.