The purpose of this retrospective cohort study was to investigate determinants of adoption of cats and dogs from a large municipal animal shelter. The subjects were 4,813 cats and 3,301 dogs impounded by the Sacramento County Department of Animal Care and Regulation and offered for adoption September 9, 1994 to May 26, 1995. The study constructed models predicting the conditional probability of adoption using logistic regression and a final multiple logistic regression model from variables found to be important predictors of adoption. Age, sex, coat color, and reason for relinquishment were major determinants of adoption in cats. Age, sex, coat color, reason for relinquishment, breed, purebred status, and injury status were major determinants of adoption in dogs. Shelter personnel could utilize this information to increase the adoption of frequently overlooked animals. Alternatively, shelters could use this to focus their resources on animals with characteristics the public prefers.