AIMS: Although studies have suggested good long-term results, arrhythmias, pulmonary hypertension and left ventricular dysfunction are mentioned as sequelae long-term after surgical atrial septal defect closure at young age. Most studies were performed only by questionnaire and in a retrospective manner. The long-term outcome is very important with regard to future employment and acceptance on insurance schemes. METHODS AND RESULTS: One hundred and thirty-five consecutive ASD-patients, operated on in childhood, were studied longitudinally with ECG, echocardiography, exercise testing and Holter-recording 15 (10-22) and 26 (21-33) years after surgery. During follow-up no cardiovascular mortality, stroke, heart failure and no pulmonary hypertension occurred. Symptomatic supraventricular tachyarrhythmias were present in 6% after 15 years, and an additional 2% occurred in the last decade; 5% needed pacemaker implantation. No relation was found between arrhythmias and type of ASD, baseline data, right ventricular dimensions, or age at operation. Left and right ventricular function and dimension remained unchanged. Slightly more patients had right atrial dilatation at last follow-up. Exercise capacity