Objective: This paper seeks to review the possibilities and difficulties in identifying rare diseases in ancient animals. Rare diseases are important in human medicine but seldom discussed in modern veterinary practice.

Materials and Methods: A total of 1348 pathological archaeozoological remains, most published in the literature, are evaluated. With the exception of a few animal burials, the majority were recovered from food refuse: deposits composed of co-mingled, single bone fragments.

Results: Determination of population-based prevalence is not applicable in animal paleopathology, as almost all lesions occur on isolated bones. Moreover, grave hereditary diseases are rarely detected on animal bones because animals with such disorders seldom survived, except when humans promoted their rare inherited traits.

Significance: Rare diseases form a special category in human pathology posing both therapeutic and ethical challenges. While in wild animals natural selection tends to prevent the inheritance of such conditions, curious cases of animal morbidity have been brought about by domestication. Humans sheltered animals of lesser vitality and sometimes even promoted their negative traits. Understanding these phenomena in animal paleopathology will help fine-tuning the rare disease paradigm.

Limitations: The definition of rare disease in animal paleopathology can only be assessed based on ancient and modern human correlates, and rare variation could become cultivated traits, ultimately developed into part of "normal" variability as trademark breed characteristics. Taphonomic limitations in recovering osteological evidence of debilitating hereditary diseases in animals are unlikely to improve.

Suggestions for further research: Further research will need to focus on the scarce osteological evidence for rare conditions in light of differential diagnoses. The concept of "rare disease" may be worth expanding beyond hereditary conditions in animals considering fundamental differences between past animal and human lifeways.