Researchers often rely on census data to provide us with information for local areas. In a study, we came across major discrepancies in rural Nepal between the number of women with a child under the age of two as estimated from the national census and the prevalence rate of this population in our local in-depth household survey. This study highlights why census data might not be as reliable as one would hope. In summary, researchers using census data in developing countries should include an element of quality control of the national dataset. We advise researchers to conduct a small survey from a random sample to provide an estimate of the likely population in the area under study.