We sought to identify which kindergarten children are simultaneously at risk of moderate or severe symptomatology in both attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD) as adolescents. These risk factor estimates have not been previously available. We conducted multinomial logistic regression analyses of multiinformant ratings by the end of middle school of a population-based, longitudinal sample of children followed from kindergarten to eighth grade (N = 7,456). Kindergarten children from low SES households, those raised by mothers with depressive symptoms or experiencing emotional problems or substance abuse, or those who were punished by spanking were significantly more likely to later display severe levels of ADHD-CD symptomatology in eighth grade. Kindergarten children frequently engaging in ADHD-CD-type behaviors were more likely to later experience both moderate (covariate adjusted OR = 2.37) and severe (covariate adjusted OR = 3.63) ADHD-CD symptomatology. Low academic achievement uniquely increased the risk of both moderate and severe symptomatology (adjusted OR range = 1.7 to 2.24). The results should guide early screening and school-based intervention efforts for ADHD-CD. Reducing children's risk for adolescent ADHD-CD symptomatology may require remediating low behavioral and academic functioning by the end of kindergarten. When these 2 modifiable factors occur together they increase kindergarten children's odds of experiencing severe ADHD-CD symptomatology in eighth grade by a multiplicative factor of 8.1.