Objective: To examine the association between cortisol levels and conduct disorder (CD) in adolescent mothers. Past research has shown that low levels of cortisol were associated with CD, particularly with its aggressive symptoms. The authors tested the hypothesis that adolescent mothers with CD would show lower levels of salivary cortisol compared to mothers without CD at 4 and 9 months postpartum. Method: Midmorning salivary cortisol levels were measured in 228 adolescent mothers (age at delivery 16.9 [+ or -] 1 years [mean [+ or -] SD]) during a laboratory visit at 4 and 9 months postpartum. CD was diagnosed during pregnancy according to the CD subsection on the criteria for antisocial personality disorder (DSM-III-R). Results: Results did not confirm the hypothesis. Lower cortisol levels were not significantly associated with a CD diagnosis, the number of CD symptoms, or aggressive symptoms. Conclusions: Despite valid measures and strong statistical power, this study failed to find an association between cortisol levels and CD in a sample of adolescent mothers. The results may have been influenced by the fact that participants were 4 and 9 months postpartum and by comparisons of mothers with CD to mothers living in stressful circumstances. J. Am. Acad. Child Adolesc. Psychiatry, 2004;43(4):461-468. Key Words: cortisol, conduct disorder, adolescent mothers.