A 39-year-old woman with documented sarcoidosis and membranous glomerulonephritis (GN) with renal failure received a kidney from her identical twin. A few months after transplantation a proliferative GN appeared with hematuria, proteinuria and progressive renal failure over 2 years. Indeed the occurrence of GN in patients with sarcoidosis raises the question of whether the relationship between these two conditions is causal or fortuitous. This report suggests that GN is secondary to sarcoidosis.