The co-occurrence of internalizing and externalizing disorders suggests that they may have common underlying vulnerability factors. Research has shown that negative affect is moderately positively correlated with both internalizing and externalizing disorders in children. The present study is the first to provide an examination of negative affect in relation to a wide spectrum of childhood internalizing and externalizing problems using a biometric model. This study extends prior findings of more narrowly focused associations by using a factor approach including multiple disorders. The sample for this study included families of 691 same-sex 7- to 13-year old twin pairs. A multifactorial independent pathway model was used to examine the genetic and environmental influences underlying the covariation of parent-reported negative affect, internalizing symptoms, and externalizing symptoms. Results of the current study suggest that negative affect shares genetic and environmental influences with both internalizing and externalizing disorders in childhood. These common influences may partially explain their comorbidity. Understanding that negative affect is at least one contributor to the covariation among these disorders may highlight avenues for early risk assessment, intervention, and perhaps prevention.