Abstract A logic-based computer program for metabolic assessment of patients with nephrolithiasis was used to evaluate 122 consecutive patients with that disease. Each patient was evaluated initially by a nephrologist, then retrospectively when more data were available. Diagnostic accuracy of computer and nephrologist were compared to the retrospective analysis, which was considered “correct”. The computer identified 94.6% of metabolic disorders present; the physician was less accurate, 81.6% ( P<0.001). Computer diagnosis of less well-defined disturbances, such as diseases responsible for calcium abnormalities, was inferior to the nephrologist (68 vs 80.5%, respectively; P > 0.1). Logic-based systems can assess exactly defined disorders, such as metabolic disturbances in stone patients, in a nearly perfect manner. When diagnostic endpoints are not well-defined, they perform poorly.