Think HIV offered HIV counseling, testing, and referral to patients at 4 Massachusetts urgent care centers from January to September 2002. We compared the positive diagnosis yield of Think HIV with that of state-funded HIV counseling, testing, and referral sites. Think HIV found an HIV prevalence of 2.0% compared with 1.9% identified by self-referral testing. Urgent care center-based routine HIV counseling, testing, and referral programs are feasible, can have high positive diagnosis yields, and should be the standard of care in high HIV prevalence areas.