OBJECTIVE--To assess the predictive impact of morphological, haemodynamic, and clinical variables in the management of patients with isolated ventricular septal defect. DESIGN--Retrospective analysis of variables by a sophisticated database management system. PATIENTS AND METHODS--263 consecutive patients with isolated ventricular septal defect diagnosed by echocardiography. The morphological type and haemodynamic character of the ventricular septal defect was characterised in each patient. In addition, variables were introduced to represent the need for diuretics, growth, and potential delay in growth. In 43 patients (16.3%) the ventricular septal defect was closed surgically; 220 patients (83.7%) were managed conservatively and spontaneous closure of the ventricular septal defect occurred in 65 (29.5%). There were no deaths. RESULTS--All patients managed surgically had non-restrictive defects and were operated on during the first year of life. A few patients with non-restrictive defects were managed conservatively. The two groups differed significantly only with respect to mean growth delay (0.65 (0.27) v 0.9 (0.21), P < 0.001). Only the morphology of the ventricular septal defect significantly (P < 0.001) influenced the probability of closure. CONCLUSIONS--Findings imply that early surgical closure of ventricular septal defect is indicated in patients with non-restrictive ventricular septal defect and severe growth delay. Other patients should be managed conservatively. In these patients the morphological type of the defect determines the probability of spontaneous closure and provides an estimate of the period over which decreased in size or closure can be expected.