Three groups of neuropsychiatric out-patients, homogeneous according to parameters of violent behaviour, were identified in a previous study using a cluster analysis procedure and compared in this study on psychometric variables. These groups were (a) a group manifesting frequent, impulsive violence (n = 35), (b) a non-violent group (n = 57), and (c) a group whose violent behaviour was much less frequent and severe than in the first group, and more provoked (n = 31). Impulsively violent patients showed language and visual-perceptual deficits, but no other neuropsychological or intellectual deficits. The MMPI F, K and Ma and MacAndrews Alcoholism scales and a perceptual organisation factor derived from the Holtzman Inkblot Test significantly discriminated groups. Results of this and the initial study have implications regarding psychological aspects of aggression and underlying biological mechanisms.