Native Americans have some of the highest rates of marijuana use and abuse, yet neurobiological measures associated with addiction to marijuana in this population remain unknown. The present investigation evaluated associations between the P350 and P450 components of the event-related potential (ERP) elicited by affective stimuli, and marijuana dependence in a population of Southwest California (SWC) Indian adults. Three hundred and seventeen participants with a mean age of 30 years who were free of major Axis I and psychiatric diagnoses and antisocial personality disorder were categorized as: (1) no marijuana use disorders or other drug dependence diagnoses; (2) marijuana dependence and no other drug dependence diagnoses; and (3) marijuana dependence and other drug dependence diagnoses. ERPs were collected using a facial discrimination task that generated a late positive component with two peaks at approximately P350 and P450 milliseconds. Multivariate analyses of variance was used to detect associations between the two component peaks and the three participant groups taking into consideration age, gender and the presence of a lifetime diagnosis of alcohol dependence. Increases in the latency of both the P350 and P450 component peaks were found to be associated with the diagnosis of marijuana dependence and marijuana dependence co-morbid with other drug dependence. Women appeared to be more impacted than men are. A diagnosis of marijuana dependence was not associated with any changes in late component amplitudes. Taken together these studies suggest that marijuana dependence may be associated with delays in the evaluation and identification of emotional stimuli in SWC Indians.