This contribution documents the individual level data preparation of burial and baptismal registers of the church books of St. James in the Hanseatic city of Rostock, Germany, in order to analyse infant mortality in the 19th century. Besides describing the digitalised registries as well as the data quality and the construction of variables this paper presents a new classification of occupations that is also applicable to other historical data sets. In addition, the merging of the baptismal and burial data into an event history data set is outlined exemplarily for the time period of 1815 to 1829. Using this data basis, the development of infant and perinatal mortality is illustrated.