Recent epidemiological data suggest that poliomyelitis is a more important public health problem in developing countries than was originally suspected. Because of the availability of a cheap, effective, but labile oral vaccine, it is important that countries determine the incidence of poliomyelitis in order to determine the necessity and speed with which a vaccination programme should be introduced.Sequelae of poliomyelitis are distinctive and can be used to study the incidence of residual paralysis in children above the age of 5 years. Prevalence data for lameness due to poliomyelitis can then be translated into rates of annual incidence of paralytic disease. Lameness surveys can be efficiently done in schools and data are reliable as long as a similar search for lame children is done amongst children of the same age group who do not attend school but are in the geographical area served by the school. House-to-house surveys, while more time-consuming, are more reliable.