An information campaign that provided Kenyan teenagers in randomly selected schools with the information that HIV prevalence was much higher among adult men and their partners than among teenage boys led to a 65% decrease in the incidence of pregnancies by adult partners among teenage girls in the treatment group relative to the comparison. This suggests a large reduction in the incidence of unprotected cross-generational sex. The information campaign did not increase pregnancies among teenage couples. These results suggest that the behavioral choices of teenagers are responsive to information on the relative risks of di?erent varieties of a risky activity. Policies that focus only on the elimination of a risky activity and do not address risk reduction strategies may be ignoring a margin on which they can have substantial impact