Previous studies have reported that State mental hospital deinstitutionalization has resulted in the criminalization of the mentally ill. Two samples of defendants found incompetent to stand trial (IST) pre- and postdeinstitutionalization were selected from three States. Changes in the characteristics of incompetent defendants were studied as well as the correlation of the rate of deinstitutionalization and frequency of incompetency commitments. Data suggest that increases in IST commitments and the mental health histories of the postdeinstitutionalization cohort are positively related to deinstitutionalization. There is no evidence that incompetent defendants are now being arrested for less serious offenses, contrary to the criminalization hypotheses. 3 tables and 30 references. (Author abstract modified)