IntroductionKidney involvement in non-Hodgkin lymphoma is recognized but mostly diagnosed following a diagnosis of lymphoma. We describe a rare case of mantle cell lymphoma, a B-cell-type non-Hodgkin lymphoma, first presenting with immune complex glomerulonephritis.Case presentationWe report the case of a 58-year-old Sri Lankan man who presented with gross hematuria. Further investigation revealed bicytopenia with splenomegaly and elevated serum creatinine. He had a renal biopsy, which revealed acute immune complex glomerulonephritis with interstitial inflammation. Results from an initial bone marrow biopsy and blood imaging were inconclusive. Three months later his renal function had deteriorated and a lymph node biopsy revealed mantle cell lymphoma. Within three months of initiating chemotherapy, his renal function returned to normal levels and remained normal at one year of follow-up.ConclusionsIt is important to have a high degree of suspicion when patients present with acute immune complex glomerulonephritis with no other identifiable cause, because it could be the first presentation of a non-Hodgkin lymphoma such as mantle cell lymphoma.