All major complications within four weeks after diagnostic cardiac catheterization (DCCA; n = 4,778) or percutaneous transluminal coronary angioplasty (PTCA; n = 3,073) were analysed prospectively in 7,851 patients (5,769 men, 2,082 women; mean age 59.4 [16-88] years). There were 116 such complications in 114 patients, 46 (0.9%) after DCCA, 70 (2.3%) after PTCA. 76% of all complications occurred during the first two days after the procedure: bleeding in 29 patients, false aneurysms in 15, arterial occlusions in 12, venous ones in three, cerebral ischaemia in 12, fulminant pulmonary emboli in three, cardiac complications in 27, and others in 15. There were five deaths in connection with a DCCA, 18 with PTCA. Complications were twice as common in women as in men (DCCA: 1.5% vs 0.7%, P < 0.05; PTCA: 4.2% vs 1.7%, P < 0.001). Complications after DCCA were more frequent in those aged over 55 years (1.2% vs 0.3%, P < 0.05); after PTCA they were more frequent in those aged over 65 years (4.1% vs 1.3%, P < 0.05). Other risk factors for complications were: peripheral arterial occlusive disease for arterial occlusion (P < 0.001), high heparin dosage with DCCA (P < 0.05), and additional venous puncture with DCCA (P < 0.01).