The aim of the paper was to analyze the records of National Census (NC) conducted in Poland with special consideration of the oldest group of the population. According to the last NC performed in 2002, the number of people over the age of 100 (centenarians) in Poland was 1544 including 1215 females and 326 males. Data from the Polish Centenarians Study, PolStu2001, enabled the authors to verify the validity of NC. A comprehensive analysis of available original personal documents and individual history of life of the subjects showed that in case of 40% of male centenarians their age was overestimated. This phenomenon was especially explicit in parts of Poland with high repatriation rate after the World War II. In Podlaskie province, the percentage of centenarians was three times higher than in other provinces of Poland. Over the years, the validity of NC data has improved, however data concerning the oldest old require scrupulous verification.