The purpose of the current study was ta examine the co-occurrence of substance abuse and three other psychiatric disorders (conduct disorder, depression, anxiety) in an incarcerated juvenile delinquent sample. Diagnostic interviews were utilized to place participants in one of three groups: No substance abuse, alcohol/marijuana abuse, or polysubstance abuse. Frequency of diagnosis and number of symptoms of three psychiatric disorders were then examined. The results indicated that the diagnosis of conduct disorder increased significantly with the occurrence of substance abuse. Also, the number of symptoms for conduct disorder, anxiety, and depression increased with substance abuse. With polysubstance abuse the probability of having more than one of the other psychiatric diagnoses was above 50%. Potential explanations for the findings, focusing on the developmental trajectory for conduct problems and self-medication for internalizing disorders, are discussed.