Abstract
We present an interesting case of a 37-year old man with acute renal failure following a febrile illness. Laboratory results showed features of macrophage activation syndrome (MAS) with anemia, thrombocytopenia, hypofibrinogenemia and elevated ferritin levels. Renal biopsy was then done to determine the cause of renal failure and showed unique glomerular findings with massive histiocytic infiltration ('histiocytic glomerulopathy') and evidence of endothelial injury. Recognizing that the histiocytic infiltrate and endothelial injury is a part of MAS is important because early recognition and treatment is of utmost importance since the disease can be fatal.