While administrative information systems can assist nurse managers to improve cost containment and resource management of their units, such effects cannot be known without rigorous evaluations. This article presents evaluation results of CLASSICA, an information system designed to provide decision support for nurse managers in financial management, resource allocation, and activity planning. CLASSICA demonstrated a 41% reduction in expenditures for overtime and extra hours during the evaluation period as compared with a 1.8% reduction in control units that did not use the system. Nurse managers reported a substantial improvement in management information and stated that they had gained control over costs. The system helped them analyse the relationships between patient activity, staffing and costs of nursing care. Nurse managers also reported high satisfaction with the system, the information and decision support provided, and its ease of use. These results suggest that CLASSICA is a decision support system that can successfully assist nurse managers in effectively managing their units.