The institutions were characterized by communal living day and night, a low degree of security, weekend leave once every 4 weeks to inmates sentenced to more than 32 days, and the opportunity to work outside the institution. Because of a shortage of space in many 'closed' institutions, some hardcore inmates from these institutions have been transferred to the half-open institutions. Data collection consisted of a quantitative inventory of the inmate population and prison incidents and of discussions with administrators and staff about inmate drug and alcohol abuse, inmate adjustment, and institutional organization. The populations of the seven institutions were similar. The average inmate age was 31, and the majority were Dutch. Half of the inmates were younger than 18 years old when they were first exposed to the justice system. Seventy-five percent of the detainees had committed three or four types of offenses. Administrators and staff perceived drug and alcohol abuse as a problem among long-term inmates. Fifteen percent of the inmates were deemed unsuitable for prison programs due to physical or psychological impairments. Staff perceived that the half-open prison was not suitable for a significant percentage of the inmates. 20 tables and 71 references.