The current trend of shorter hospital stays has heightened concern about the adequacy of preparation of patients and their families to understand and follow prescribed medication regimens properly following discharge. Cooperative Care, an education-intensive unit incorporating a living-in family member or friend acting as a 'care partner,' has had a self-administration of medication program (SAM) for the past 16 years. This paper describes SAM and reports on two studies of its effectiveness. The first was a 1-week survey of all patients (151) admitted to the unit. 126 (83.4%) were taking a mean of five medications, with a range of one to 17. Of those, 102 (80.9%) were able to participate in SAM independently, and 11 (8.7%) were on SAM with supervision by their care partners. The second study reviewed medication administration errors within Cooperative Care and the traditional nursing units of Tisch Hospital over a 4-year period (1991-1994). Cooperative Care accounted for 19.4% of discharges (22,164/114,206) and 10.3% of patient days (97,037/944,230), but only 4.6% of medication errors (80/1723). The medication error rate per 1000 discharges was 3.6 for Cooperative Care, and 17.8 for the traditional units. Comparative error rates per 10,000 medication orders were 3.06 at Cooperative Care and 4.01 on the traditional units. 74.8% of Cooperative Care patients were on SAM, but only 30% of the errors were attributed to patients or care partners. The other errors were attributed to nursing staff (50%), equipment defects (12.5%) or pharmacists (5%). Our data indicate that SAM during hospitalization is a safe and effective modality of care.