: IgA nephropathy IgAN is characterized by mesangial deposition of IgA, C3, and often IgM. We examined the relationship among IgM deposition, clinical features, and renal outcome in IgAN patients who underwent combined treatment of tonsillectomy with steroid pulse therapy Tx-SP . We retrospectively reviewed 73 IgAN patients treated with Tx-SP from March 2006 to March 2014. The patients were divided into those with moderate 2 to severe 3 mesangial IgM deposition Prominent IgM-positive patients, P-Group and those with negative to faint 1 deposition the Other patients, O-Group . Using propensity scores to minimize confounding factors, 11 propensity score-matched patients with O-Group mO-Group were compared to 11 P-Group patients. The study out come was de ned as urinary protein grade by urine test strip before Tx-SP and one year after Tx-SP. P-Group patients exhibited an increased severity of protein uria compared to O-Group p 0.018 and mO-Group patients p 0.009 before Tx-SP. After Tx-SP, proteinuria was signi cantly ameliorated in the P-Group, reach ing the same severity recorded in the O-Group p 0.007 and mO-Group p 0.021 . No signi cant differences were noted between P-Group and mO-Group in microhematuria, serum creatinine level, and histological severity. Prominent IgM deposition is associated with severe proteinuria in IgAN. However, Tx-SP induces a suf cient reduction in the severity of proteinuria in IgM-positive IgAN.