A prospective study was undertaken to assess the value of ultrasonography in the clinical monitoring of angiomyolipomas. 26 patients with angiomyolipomas as diagnosed by sonography and verified by computerized tomography (CT) were followed up by sonographic monitoring over a mean period of 45 months. One case was associated with tuberous sclerosis. Inclusion criteria for conservative management had been clinically asymptomatic angiomyolipomas smaller than 5 cm. Significant tumor growth and a change of the sonographic pattern during follow-up was seen in 2 patients. After renewed follow-up CT scanning failed to reveal negative density values, both patients were nephrectomized. Histologic examination showed hemorrhage in the tumor. The remaining 24 patients (92%) showed no changes in the sonographic patterns. Minor tumor growth of 0.5 cm on average was seen in 6 patients over a mean follow-up period of 52 months. Surgical intervention was refrained from in these 24 patients due to the consistent sonographic pattern and the absence of clinical symptoms. Once the angiomyolipoma is verified by CT, sonographic monitoring suffices if the sonostructure remains unchanged. Minor asymptomatic angiomyolipomas today no longer require surgical intervention as this benign tumor has a pathognomonic sonographic appearance.