Inherited hemolytic-uremic syndrome (HUS) is unusual. We report the occurrence of HUS in two siblings; one died at an early age while the other (the proband) has presented with three episodes of HUS since the age of 19 years. The finding of a persistently low serum C3 level in this patient led to a thorough evaluation of her complement cascade and a family investigation. The proband and her asymptomatic younger sister were found to have very low serum levels (5% of normal) of factor H, a regulatory protein of the alternative complement pathway. Both patients had low levels of serum C3, factor B, CH50 and VAH50, reflecting persistent alternative pathway activation. The father and mother both had half-normal serum factor H levels but an otherwise normal complement profile. Other members of the extended pedigree were also found to have half-normal serum factor H levels. In conclusion, in this family, factor H deficiency appears to be associated with HUS and is transmitted as an autosomal recessive trait. Persistent C3 hypocomplementemia in the setting of familial and/or recurrent HUS should be a clue to a possible inherited complement deficiency.