The relationship between animal ownership and owners' health has received increasing attention in the recent human-companion animal literature. This article considers a new aspect of the human-companion animal relationship, that of compatibility between pet and owner. Compatibility is viewed as the fit between the animal and the owner on physical, behavioral, and psychological dimensions. A postal survey was used to test the hypothesis that compatibility has influences on physical and mental health that are independent of those due to owners' level ofpet attachment and human social support. A sample group of 176 pet owners completed a questionnaire containing a new measure of compatibility as well as standard measures of pet attachment, human social support, and mental and physical health. Results of multiple regression analyses indicated that people who are relatively more compatible with their pets report better mental health overall and fewer physical symptoms. Social support was positively associated with mental health. Pet attachment was also positively associated with mental health, but negatively with physical health.