We studied glomerulonephritis in a child with a deficiency of the second component of complement (C2) who was without clinical or serologic evidence of systemic disease. The clinical course was severe, with malignant hypertension and terminal renal failure when the child was 14 years old. Results of histologic studies were typical of membranoproliferative glomerulonephritis with subendothelial deposits. Immunofluorescence microscopy showed diffuse and intense localization of IgG, C1q, and C4 as granular deposits along the glomerular capillary walls and within the mesanguim. Diffuse deposits of C3 were also found along the capillary walls. Nine months after transplantation, the graft biopsy specimen showed glomerular lesions with IgG, C1q, C4, and C3 deposits, which suggests the possibility of a recurrence. The analysis of the previously reported cases of glomerulonephritis with C2 deficiency showed variable, but generally mild, glomerular lesions. Progression of the glomerulonephritis to severe renal insufficiency, as in the present case, is exceptional.