During a 10-year period, intraparenchymal aneurysms were found in 38 of 748 patients at selective abdominal angiography with magnification technique. According to strict criteria, 17 patients were classified as suffering from necrotizing vasculitis of the polyarteritis nodosa group (PAN), 7 from severe arterial hypertension, and 3 from rheumatoid arthritis. The diagnoses of 5 patients remained to be confirmed, and each of the remaining 6 patients suffered from various other diseases. PAN was diagnosed histopathologically in 2 patients without angiographic aneurysms. Based on the 156 patients in whom the indication for angiography was suspicion of arteritis, the angiographic diagnosis of PAN had a sensitivity of 89 percent and a specificity of 90 percent, a positive predictive value of 55 percent and a negative predictive value of 98 percent. The mean number of both renal and hepatic aneurysms was higher in patients with PAN than in the other patients (p less than 0.01 and p less than 0.05, respectively). Five PAN patients had numerous and large aneurysms, whereas the aneurysms of the other 12 PAN patients did not differ from those of patients with other diseases. Patients with PAN had renal infarcts more often than the other patients (p less than 0.05). Our findings suggest that visceral angiography is useful in establishing the diagnosis of PAN, but the angiographic finding of aneurysms is not pathognomonic.