The monastic book of the deceased Cistercians of Koronowo has been preserved in a copy believed to have been made by Maciej Rajmund Garczyński in 1717. Entries continued to be made in it until 1810. Its reliability can be checked against other documentary sources such as the "Liber Confratrum" and the Book of Monastic Professions available to us from a volume which came into use in 1764. Since the Koronowo register of the dead comprises also obituary entries of religious from other orders, a comprehensive study of its contents would require a survey of sources from other convents and their backgrounds. The register lists 312 monks from Byszewo and Koronowo. The earliest record mentions Abbot Mikołaj, who died in 1253; the last — cantor Jan Jasiński, d. 1810. While medieval and 16th-century obituary notes seem to be based on other sources, those compiled in the 17th and 18th centuries are more numerous. There are notable discrepancies between Series abbatum and corresponding entries on the abbots in the monastic register. The inconsistencies concern both the abbots themselves as well as the chronology of their officeholding. Beginning with Abbot Adam Mirowski (1549-1567), the two sources display no more discrepancies, apart from a few minor divergencies in the dating of some abbots’ deaths. In the case of other monastic officials, the register as a rule does not mention their official functions. The fact that the obituary notes contain nothing but names makes further identification of the dead monks practically impossible. Nevertheless, it has been possible to identify twelve priors and a few deputy priors, cantors, and masters of the novitiate. Such information appears more often in the Byszewo entries. Sometimes the notes contain something of an educational attainment of the Koronowo monks. To judge by the register, the mortality rates at the Koronowo convent were perceptibly affected by the epidemics and wars of the 17th century. In the 18th century, however, natural disasters (including the ravages of the Northern War) seemed to have no such impact on the death rate at the convent. Taking the register as a source, no period in the history of the convent was as disastrous as the decade 1621-1630. Even though our data are incomplete, there can be little doubt that those were the convent’s darkest days. In the 18th century, which is relatively best documented in our sources, most deaths seem to have occurred in March, April, May, and June, while the fewest inhabitants of the convent died at the end of autumn and the beginning of winter, i.e., in November and December.