Smoking cessation among pregnant adolescents remains a complex and unresolved issue. The purpose of this study was to examine adolescents' knowledge of the detrimental effects of smoking on pregnant women and fetuses and its relationship to efforts to quit smoking. The sample consisted of 71 pregnant adolescents, and a three-group randomized intervention design-Teen FreshStart (TFS), Teen FreshStart with buddy (TFSB), and usual care control (UCC)-was used. Instruments included a demographic questionnaire, a smoking history questionnaire, and an 11-item scale measuring knowledge of the effects of smoking during pregnancy. For the entire sample, knowledge scores increased significantly (p = .000) from T1 (preintervention) to T2 (postintervention), and the adolescents who quit smoking had significantly higher knowledge at T2 (p = .028) and greater increases (T1 to T2) in their knowledge (p = .019) than did those who did not quit. Together, the TFS and TFSB groups had significantly higher knowledge at T2 (p = .017) and a significantly greater increase in knowledge from T1 to T2 (p = .005) than did the UCC group. This also held true when the TFS and TFSB groups were examined individually. Each had significantly higher knowledge at T2 (TFS, p = .029; TFSB, p = .008) and a significantly greater increase in knowledge from T1 to T2 (TFS, p = .007; TFSB, p = .009) than did the UCC group. Furthermore, despite the small sample sizes, within-group comparisons showed (a) no significant differences between quitters and nonquitters in the UCC group, (b) significantly higher knowledge at T2 (p = .052) and a trend indicating greater increases in knowledge from T1 to T2 (p = .092) for the quitters compared with the nonquitters in the TFS group, and (c) a trend for adolescents in the TFSB group who quit smoking to have greater increases in knowledge compared with those who did not quit (p = .158). These results indicate the need for continued inquiry into the relationship between pregnant teenagers' health knowledge and decisions to stop smoking.