A 14-year-old boy with C3 glomerulopathy and Sjögren's syndrome identified by a school urinary screening program.

C3 glomerulopathy (C3G) is a type of complement-associated glomerulopathy caused by a defect in the alternative complement pathway and is regarded as a rare disease. We report a 14-year-old boy with C3G and Sjögren's syndrome (SS) whose school urinary screening revealed abnormalities, but the diagnosis was delayed because he refused to consult a medical institution. Histopathological examination revealed histologic features of membranoproliferative glomerulonephritis. He was diagnosed with C3G and Sjögren's syndrome based on proteinuria, the histopathological findings, high levels of antibodies against SS-A, and lymphocytic infiltration around the salivary glands. He was treated with combination therapy, consisting of methylprednisolone pulse, prednisolone, and mycophenolate mofetil. At 3 months after treatment, urinary protein excretion was decreased and hematuria had disappeared, and improvement in hypocomplementemia and the levels of antibodies against SS-A were observed. The course of our case suggests that the management of patients with C3G should take into consideration the possibility of the coexistence of SS, and that those with positive findings on school urine screening should be encouraged to visit a medical institution.