The goals and purposes of IDRA 1980 are reviewed, and the implementation of the legislation is traced through a statistical review of some of the changes associated with the Act. Three cohorts are comparied and analyzed. The earliest consists of persons acquitted 'by reason of mental disease or defect' between 1971 and 1976; this cohort provides data on conditions of confinement over time. Two cohorts of acquitted individuals, one under the old law which existed just prior to IDRA, and one under IDRA 1980, are traced and compared. The data suggest that IDRA has had the effect of formalizing, regularizing, juridicizing, accelerating, and extending to all acquittees a procedure that was in place before the passage of the legislation. Although more persons are reviewed under IDRA and more persons are released at postacquittal hearings, fewer enter nonsecure facilities at the commitment stage, fewer move from secure to nonsecure facilities during the first 18 months of their hospitalization, and fewer are released at the 6-month review stage. IDRA is found to have put tighter controls on persons designated as being dangerously mentally ill at their postacquittal review hearing. Approximately 45 references, 25 tables, and 7 appendixes are included.