Low serotonin has been associated with aggressive behavior and impulsivity. Executive functions (cognitive abilities involved in the initiation/maintenance of goal attainment) have also been related to aggression. We tested whether dietary depletion of tryptophan, the amino acid precursor of serotonin, would increase disinhibition (impulsivity) in aggressive male adolescents. Cognitive-neuropsychological variables predictive of disinhibition were explored. Stable aggressive and nonaggressive adolescent men received balanced and tryptophan-depleted, amino acid mixtures separately (counterbalanced, double-blind). Commission errors on a go/no-go learning task (i.e., failures to inhibit responding to stimuli associated with punishment/nonreward) measured disinhibition. Aggressive adolescent males made more commission errors as compared to nonaggressives. Lower executive functioning was significantly related to commission errors over and above conventional memory abilities. Tryptophan depletion had no effect on commission errors in the aggressive adolescents, possibly because of a ceiling effect.