The possibility of closing an atrial septal defect in adults by means of a percutaneously introduced catheter with an umbrella-type occluder was tested in seven consecutive patients with this defect (two men and five women, aged 35 to 69 years). The diameter of the defect (echocardiographic measurement) ranged from 7 to 25 mm, the left to right shunt from 11% to 54% of pulmonary flow and the pulmonary artery pressure from 24/8 to 110/25 mmHg. In one patient no attempt was made to close the defect because of its size (invasively measured: 40 mm). In another patient the method failed. Closure was successful in four of the patients (left to right shunt < 5%), while in a fifth patient a haemodynamically significant residual shunt (38%) remained, but was closed 2 months later with a second occluder. In one of the patients a portion of the device embolized to the pulmonary artery from which it was removed by catheter.--Thus the intervention was successful in five of six patients. This experience suggests that this type of occluder can also be used successfully in adults.