Eight-six children with meningococcal meningitis or bacteremia were evaluated prospectively between 1977 and 1979 to determine the incidence of complications and features predictive of their development. The majority (83%) of these infections were caused by serogroup B strains. Twenty-seven percent of survivors experienced one or more suppurative, allergic, or neurologic complications. Hearing loss, noted in 9% of children, occurred significantly more often in patients with admission leukocytosis or leukopenia, or with CSF leukocytosis greater than 10,000/mm3 than in those with an uncomplicated course (P less than 0.01). Ten percent of survivors developed allergic complications manifested as cutaneous vasculitis or arthritis with onset five to eight days after admission. Shock, purpuric skin lesions, and fever persisting longer than five days occurred significantly more often in these children than in those who developed hearing loss or those with an uncomplicated course (P less than 0.05). Resolution of allergic complications occurred within 14 days of their onset. Compared to Neisseria meningitidis groups A and C, group B strains appear to be intermediate in their potential for allergic complications associated with childhood infection.