The cost effectiveness of various modes of family planning service delivery based on the cost per couple-year of protection (CYP) is assessed using 1984 data for 63 projects in ten countries (three each in Africa and Asia, and four in Latin America). More than 4.8 million CYPs were provided through these projects during the year studied. Programmes with the highest volume of services delivered corresponded to lowest average costs: social marketing (2.8 million CYPs) and sterilization projects (960,000 CYPs) cost about $2 per CYP, on average; highest costs were for full service clinics and community-based distribution projects ($13-14 per CYP). Costs of clinics combined with community-based distribution services fell approximately midway between these two extremes.