Students in their clinical clerkship performed retrospective reviews of their peers' laboratory usage patterns. Data covering the patient's history and physical examination, problem list, and treatment plan had been completed by students during internal medicine and pediatrics rotations. This information, along with the first day's diagnostic orders, was provided to community medicine clerkship students who then evaluated the cost and medical necessity of diagnostic tests ordered in light of the problem information. Application of such cost control programs, before students form definitive conceptions of treatment, may contribute to more cost-conscious behavior in their future medical practice.