In this clinicopathological conference, an 11-year old boy who presented with recurrent pyogenic infections, hypertension, malar rash, various skin lesions and nephritic syndrome since five years of age is discussed. He was hospitalized for clinical investigation with skin and renal biopsies at 10 years of age. Using clinicopathological data obtained from his last admission, a clinical diagnosis was reached, and the disorders of the complement system causing patients to show these signs or symptoms are emphasized. At the end of the discussion, a clinicopathological correlation is given for making the diagnosis.