Psychoticism is the dimensional alternative to the categorical concept of psychosis. In this study we examined this psychoticism dimension and its validity. Psychotic and nonpsychotic patients received various self-rating scales measuring psychoticism, extraversion and neuroticism, a structured interview, and were rated on a scale for psychotic(-like) experiences. Scores on the self-rating scales were factor analyzed. Psychoticism emerged as a clear factor. It correlated significantly with symptom scores and the various diagnostic groups were significantly different only on this factor. The other factors were extraversion, neuroticism and impulsivity-rigidity. These factors are less important in describing psychotic disorders, but nevertheless they tap clinically relevant aspects.