The article examines the issue of illegitimate birth (defectus natalium) among clergy in late medieval Prussia. As one of the irregularities under canon law (irregularitas), it posed a barrier to ordination. However, papal dispensations offered a potential solution, typically granted by the Apostolic Penitentiary. This study primarily focuses on dispensations obtained through this route. The analysis of twenty-one supplications from Prussian dioceses spanning 1431–1523 reveals a significantly lower number compared to the rest of Europe, which was likely influenced by Prussia’s peripheral status, church structures, legal awareness, and the scope of interactions with the Holy See. The article also explores the social demographics of those seeking dispensations, noting a prevalence of scholars. Additionally, it examines the status of parents of illegitimate clergy candidates. Seven of them were from lay relationships of single state (solutus/soluta), two from relationships of a man of single state and a married woman (solutus/coniugata), while 12 were descendants of priests. The discussion of illegitimate births of clergymen and their efforts to obtain dispensations is enriched by a detailed examination of the case of brothers Albert and Kirstan from Ostrowite in Gdańsk Pomerania, sons of a local parson who sought dispensation for ordination. In 1380, they successfully obtained dispensation from the Apostolic Penitentiary, later approved by the Archbishop of Gniezno as their proper ordinary. The article includes two documents from the State Archives in Toruń related to this case, contributing significantly due to the scarcity of such sources, exacerbated by the absence of preserved files from the Apostolic Penitentiary during this period.