Cost-effectiveness studies were carried out in The Gambia to estimate costs of preventing childhood morbidity and mortality through immunization. For the four priority diseases--neonatal tetanus, pertussis, measles and poliomyelitis--costs per case prevented ranged from $1.30 for pertussis to $655.54 for poliomyelitis. In terms of preventing childhood deaths through immunization, measles at $40.83 per death prevented, pertussis at $99.85 per death prevented and neonatal tetanus at $152.53 per death prevented were most cost-effective. For developing countries, immunization is an efficient use of limited health resources.