A congenital C5 deficiency was the cause of recurrent meningococcal di
sease in a 27-year-old man. The lack of serum bactericidal activity ac
counts for the higher incidence and the different course of Neisseria
infections in patients with a deficiency of the late complement compon
ents. Early antibiotic treatment and vaccination with a capsular polys
accharide meningococcal vaccine (A,C,Y,W-135) should be considered.