Estimates of canine and feline euthanasia at U.S. animal shelters--largely based on voluntary surveys with low response rates--make it difficult to estimate the population from which the euthanized animals derive. Estimates of euthanasia rates (animals euthanized per unit of population) have varied widely and been available only sporadically. This study used requirements of Michigan state law (Pet Shops, Dog Pounds, and Animal Shelters Act, 1969) for animal shelters to collect admission and discharge data for all 176 Michigan-licensed animal shelters. In 2003, Michigan shelters discharged 140,653 dogs: Of these, 56,972 (40%) were euthanized; 40,005 (28%) were adopted. This annual euthanasia rate is 2.6% of the estimated 2003 Michigan dog population. Michigan shelters discharged 134,405 cats in 2003: 76,321 (57%) by euthanasia and (24%) by adoption. The estimated ratio of euthanized cats to cats who had owners was 3.1%. Small shelters and privately owned shelters were associated with higher adoption rates. Comparison with historical information from the past 10 to 20 years suggests the number of companion animals being euthanized in shelters has decreased and that progress has been made in reducing the companion animal overpopulation problem.