The occurrence of glomerular capillary aneurysms in light-chain nephropathy and a morphologic pattern of development as determined by electron microscopy are described. Renal biopsies from 4 patients with nodular glomerulopathy were evaluated. Light-chain deposition in mesangium and capillary walls was associated with monocyte accumulation in capillaries. Loss of endothelial cell lining and disruption of mesangial anchoring points of basement membranes ensued, resulting in aneurysmal dilatation of the capillaries. The walls collapsed, and the aneurysms healed as a result of mesangial interposition, a process which, in combination with enlarging nodules, led to thickening and collapse of the walls and narrowing of the lumens. This study, in conjunction with review of photographs from previously published reports, indicates that glomerular aneurysms are a common feature of nodular light-chain glomerulopathy. It also emphasizes additional light-microscopic similarities between this glomerulopathy and nodular diabetic glomerulosclerosis.