Boys consistently have expressed more negative attitudes toward women in science than have girls. The basis of these negative male attitudes was explored in a sample of 159 male and 158 female science-oriented high school students. The students participated in a science enrichment program in which positive information about women in science was provided. Consistent with theories of prejudice and stereotyping: (a) at the beginning of the program, more negative attitudes toward women in science were linked to lower science self-confidence among boys, but not among girls; and (b) following the program, analysis of residual post-scores (with pre-scores controlled) indicated that changes in self-confidence over the course of the program were related significantly to changes in attitudes toward women in science among boys but not among girls. Implications for girls’ and women's participation in science are discussed.