The purpose of the study was to show the differences in mortality in Catholic and Lutheran communities of the 19th-century Greater Poland (Wielkopolska) and its causative factors. Data on mortality were derived from two sources: 1) parish death registers, 2) vital statistics from von Bergmann’s monograph. The values of CDRs for Lutherans and Catholics were 29.25 and 31.74, respectively. Infant mortality was also lower in Lutheran populations than in Catholic ones: 258 to 296 infant deaths per 1,000 live births. Higher mortality of Catholic children than Lutheran ones was confirmed by higher values of the Crow’s index in the former than in the latter. Life expectancy of a newly born child in Lutherans was 35 years, while in Catholics 4 years lower. Differences in mortality between Catholics and Lutherans in Greater Poland in the 19th century were caused by various factors one of which was religious denomination.