The Bangladesh Bureau of Statistics (BBS) has been conducting nutrition surveys of young children at 2-3-y intervals since 1985. However, data on malnutrition determined on the basis of weight-for-age and height-for-age in different surveys are inconsistent. OBJECTIVE: The aim of this study was to investigate the reasons for inconsistencies in the findings of these surveys. DESIGN: Although the regular personnel of the BBS collected data on anthropometry and age in the previous surveys, 1995-1996 data were collected by locally recruited workers. Data on 100 children included in the 1995-1996 survey were also independently collected by BBS personnel. A comparison of the data from these 2 sources and the inconsistencies therein form the basis of this study. RESULTS: The average difference between the 2 sources (bias) was found to be approximately 1.8 mo for age and 0.13 cm for midupper arm circumference. Differences in weight and height were negligible; however, random error was found to be substantial in data on height. CONCLUSIONS: Bias in age was thought to be mainly responsible for the inconsistencies in the measures of malnutrition in the different child nutrition surveys in Bangladesh. A method for accurately collecting age data needs to be developed on the basis of a study in a demographic surveillance area where accurate age data are available. Until such a method is fully developed, midupper arm circumference should be routinely collected in all nutrition surveys. The importance of accuracy in weight and height data is emphasized