A 51-item true-false Impulsive Nonconformity Scale was constructed to measure impulsive antisocial behavior of the sort often reported in the premorbid adjustment of some psychotics. Schizophrenics and schizoaffective patients (N = 46) scored higher on the scale than control (N = 76). An experimental group of 120 aberrantly high-scoring (2 SDs above the mean) college students and 176 control subjects were interviewed using modified versions of Weissman and Paykel's Social Adjustment Scale interview and Spitzer and Endicott's Schedule for Affective Disorders and Schizophrenia-Lifetime Version (SADS-L). The experimental subjects reported more antisocial and nonconforming behaviors than control subjects, supporting the construct validity of the scale as a measure of impulsive nonconformity, and reported more psychotic or psychotic-like experiences, more schizotypal experiences, and more depressive and manic or hypomanic symptoms, suggesting that a portion of the experimental subjects may be at elevated risk for psychosis and/or major affective disorder. Subjects who score aberrantly high on both the Impulsive Nonconformity Scale and our earlier Perceptual Aberration-Magical Ideation Scale are more aberrant on several other measures of schizophrenic-like cognitive slippage than are subjects who score high on only one of the two scales.