The goal of this thesis was to identify the most common causes of neonatal pathology in puppies leading to death within the first three weeks of life. The neonatal period is a very sensitive time during which the puppy is completely dependent on the mother and is unable to live independently. Complications may already occur during birth, and until the puppies develop their immune system, death from various bacterial and viral infections is a threat. Other than environmental factors, survival also depends on the puppy itself. Inherent malformations and disorders represent major obstacles to survival. Depending on their scope, the organs and organ systems affected, some pathological processes only exacerbate the conditions for survival, while some cause deaths immediately after birth or within the first days of life. An examination of the database from the Department of Pathology revealed 35 cases of neonatal pathology in puppies with fatal outcomes. The data was sorted by the cause of death (histopathological diagnosis) into deaths caused by viral infections, bacterial infections, deaths due to a congenital disorder or malformation, deaths due to aspiration of amniotic fluid or some foreign content, and other causes that have occurred as isolated (individual) cases or it was not possible to determine with certainty the exact cause of death. The respective cases found in the database were sorted by the aforementioned groups together with information about age, breed, sex and owner, as well as the number of deaths in the same litter (if available). The results obtained were compared with previous findings, studies of other authors and their conclusions. The results of our study indicate that the most common cause of neonatal death of puppies is an infection caused primarily by viruses, followed by bacteria. In such cases, several deaths in same litters were also recorded. Congenital disorders and malformations have generally occurred in cases of breeding purebred dogs with a genetic predisposition. In some cases, overlaps in causes of death have been identified, such as the aspiration of amniotic fluid or foreign contents. In some cases, the aspiration itself did not cause death, but rather served as a background for a secondary infection which led to the death of puppies. Our results are similar to those in previous studies, and indicate that there are no significant differences between causes of neonatal puppy mortality in our region when compared globally.