The aim of this prospective study in Morocco was to investigate the causes of invasive bacterial diseases in children in order to inform antibiotic therapy and vaccine choices. Of 238 children aged < or = 5 years admitted to the Children's Hospital of Casablanca for invasive diseases over a 12-month period, 185 were diagnosed with bacterial infection: 76 had chest-X-ray-confirmed pneumonia, 59 had meningitis and 50 had sepsis. Streptococcus pneumoniae was the most common pathogen identified (n = 24), followed by Neisseria meningitidis (n = 18, all group B) and Haemophilus influenzae (n = 11). The rate of penicillin non-susceptibility was 62.5% among Str. pneumoniae isolates and 11.1% among N. meningitidis and all isolates were ceftriaxone-susceptible. Of the 11 H. influenzae isolates, only 1 produced a beta-lactamase. The 5 predominant Str. pneumoniae serotypes were 19F, 14, 23F, 6B and 19A and the theoretical coverage of the 7, 10 and 13-valent pneumococcal conjugate vaccines was 60%, 78% and 91% respectively.