The Census of 1872 contains relevant inconsistencies among young ages. We identified these problems, for the parishes of the Município Neutro and the Province of Rio de Janeiro, through the use of general demographic patterns: the sex ratio at birth and the proportions among the number of person-year lived during the first years of life, according to the life table Brazil 1870-1890. The inconsistencies among the data for each sex, in the young ages, and in the relative proportions among ages, for each sex, are clear. Furthermore, we show the great diversity of forms and intensities of these incoherencies among parishes. As a consequence, we believe that, to be precise, any historiographical analysis based on the data of the Census of 1872 requires previous adjustment of the totals published for young ages.