A total ban on all tobacco products was implemented in a diverse psychiatric institution. A post hoc evaluation examined the effect of the ban on long-term patients by comparing their characteristics the year before the ban to the year after. Several variables measuring physical health, psychiatric symptomatology, feelings of well-being, and interpersonal conflict were coded with very high reliability from health records. For the majority of patients who were in the maximum security forensic division, the tobacco ban was associated with almost no detectable ill effects with some clear benefits. Among the remainder of the long-term patients, the ban might have been associated with a temporary increase in physical aggression towards staff members. It was concluded that successful implementation, and the avoidance of ill effects, depended entirely on the success staff members had in actually preventing patient access to tobacco.