A critical evaluation of the available data on migration between India and Pakistan in the 1951–61 decade leads to the conclusion that there was a substantial net migration of Pakistan-born persons into India, but only a negligible net migration of India-born persons into Pakistan. Annual administrative statistics published by the Indian Government suggest an immigration from Pakistan of the order of 1.16 to 1.32 million. More importantly, birthplace data from the Indian censuses indicate a net intercensal immigration of Pakistan-born persons amounting to 1.19 to 1.34 million, depending on the assumed level of mortality. The Pakistani census data on the India-born show no net influx from India during 1951–61. Intercensal growth rates for the populations of different religious faiths in Pakistan are consistent with the estimates of net immigration into India. The migrants and the survivors of their progeny are estimated to represent a net gain of about 1.68 million by India and to account for no more than 2.2 per cent of the total population growth in India during 1951–61.