While deficiency of the terminal components of complement (C3–C8) has classically been associated with recurrent pyogenic infections, it has become apparent that C2 deficiency is also associated with recurrent infections in some individuals. The patient presented here had two major pyogenic infections prior to 1 year of age and was found to lack the second component of complement. Studies of alternative complement pathway and humoral and cellular immunity were found to be within normal limits. Family studies suggest an autosomal codominant pattern of inheritance for the C2 defect, which also corresponded to the inheritance of the HLA A10 B18 haplotype. A review of the literature revealed nine other cases of C2-deficient patients with well-documented recurrent infections. In these patients,Streptococcus pneumoniae is the organism most frequently implicated in infectious processes, whether or not their alternative complement pathway is intact.