Five adults had infection caused by Neisseria meningitidis serogroup W135. Their ages ranged from 19 to 74 years, and the spectrum of illness included meningitis, pneumonia, and acute peritonitis. Two patients had systemic lupus erythematosus and were receiving corticosteroids at the time of their infection. One patient died of fulminant meningococcemia. All isolates were sensitive to sulfonamides. The recent increase in the national incidence of N meningitidis serogroup W135 infections emphasizes the need for continuing surveillance and justifies its inclusion in a polyvalent meningococcal vaccine.