Purpose of study: Congenital division of an atrium is commonly associated with other cardiac malformations, which may influence presentation. Basic methods: Cases diagnosed at our institution between 1980 and 1997 were reviewed, to determine whether associated lesions influence presentation. Principle findings: 52 patients were diagnosed with atrial division (49 left. 3 right), mean age 4.8 yr. Patients could be divided according to age at diagnosis. Group 1: 32 patients aged ≤ 1 yr. 14 patients had associated cardiac malformations other than atrial septat defect (ASD). Presentation was with pulmonary oedema. Group 2: 20 patients > 1 yr. 5 patients had associated major malformations other than ASD Commonest presentation — Isolated shortness of breath. Fifty patients underwent membrane resection and correction of associated anomalies (4% mortality) At follow-up (mean 12 yr) all patients were in NYHA class 1 or 11. Conclusions: Patients with division of the atrium present early in infancy and with more severe symptoms when associated with other cardiac malformations.