A few cases of improvement in secondary renal amyloidosis following surgery (in particular, removal of the amylogenic foci) have been published, but cases of aggravation are much more numerous. The authors report on three patients whose renal function deteriorated dramatically after extra-renal surgery (pneumonectomy, aortic valve replacement, mitral valve replacement). None of the usual precipitating factors, such as DIC, cardiovascular collapse, sepsis or renal vein thrombosis, could be detected, but two patients had been under extracorporeal circulation. Such accidents appear to be unpredictable and irreversible. They can be seen in primary or secondary amyloidosis and whether or not surgery involves an amylogenic focus. Indeed, in two of their patients the diagnosis of amyloidosis was unknown before the operation. This suggests that in patients with suspected amyloidosis no major surgical operation should be undertaken without prior renal biopsy.