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Populations of unowned free-roaming cats existthroughout the world. Concern about the impact of free-roaming cats on the environment and public health, as well as consideration of the welfare of the cats themselves, has led to various efforts to reduce their numbers. After decades of effort, free-roaming cats have been extirpated from several small, uninhab-ited islands as a result of intensive control measures, including poisoning, hunting, trapping, and introduc-tion of infectious feline diseases.1-4 Despite the success of eradication campaigns on geographically isolated islands, logistic barriers and opposition from resident citizens often make application of such strategies to populated mainland territories unfeasible.4-10 Cat con-trol programs in populated areas must incorporate safety considerations for nontarget animals and humans, be affordable for participating municipal agencies or charitable organizations, include plans to curtail continuous cat immigration and reproduction, and be aesthetically acceptable to the public.4 The number of unowned free-roaming cats in the United States is unknown, but is suspected to rival that of pet cats (73 million in 2000) and to contribute sub-stantially to cat overpopulation.11-14 The free-roaming cat population consists of both socialized stray cats and unsocialized feral cats. Individual cats may have a vari-ety of lifestyles during their lives, including owned pet, stray, and feral status. Because of the vast overlap of lifestyle and socialization status continuums, it is diffi-cult to define discrete populations of free-roaming cats.15 Considerable controversy surrounds methods for controlling free-roaming cats, particularly identification of the option that is most practical, effective, and humane. Trap-neuter-return (TNR) programs are intended to halt reproduction without causing harm to the cats.7,10,16-18 In this approach, cats are trapped, neutered, returned to the site of capture, and released. Veterinarians are central to the process, because they per-form the surgeries and are frequently asked to consult on issues of health and welfare of free-roaming cats. The concept of TNR as a humane method for cat population control is endorsed by the AVMA19 and many humane organizations.10 More than 1,000 veterinary members o