This study investigates the patterns of recording birth weight data in retrospective surveys and their influence on birth weight estimates in less developed countries. We hypothesise that the method of reporting birth weight in surveys influences the classification of infants in the low birth weight category. Population-level data from Demographic and Health Surveys conducted in six selected countries representing different regions of the world were used. Birth weight data were reported in the survey from either an official health card or from mother’s memory. Birth weight distributions were examined in detail and revised low birth weight estimates were calculated accounting for potential heaping and data inconsistencies. There were substantial differences in the distribution of birth weights by method of reporting. The percentage of infants with low birth weight was higher in all six countries for birth weight recalled from memory than when reported from a health card. Health cards displayed less clustering on certain digits than memory recalled weights, but were still highly heaped in certain countries. Heaping of birth weight data on multiples of 500 g was also observed irrespective of any differences in method of reporting. The study concludes that the method of recording birth weight data can affect birth weight estimates in developing countries. Health systems in poor countries should initiate efforts to systematically monitor the recording of birth weight data ensuring for both quality and comparability at the international levels.