Mexico has cultivated opium poppy since before the 1900's and has been an important transit route for South American cocaine for decades. However, only recently has drug use, particularly injection drug use, been documented as an important problem. Heroin is the most common drug used by Mexican injection drug users (IDUs). Increased cultivation of opium poppy in some Mexican states, lower prices for black tar heroin and increased security at U.S.-Mexican border crossings may be contributing factors to heroin use, especially in border cities. Risky practices among IDUs, including needle sharing and shooting gallery attendance are common, whereas perceived risk for acquiring blood borne infections is low. Although reported AIDS cases attributed to IDU in Mexico have been low, data from sentinel populations, such as pregnant women in the Mexican-U.S. border city of Tijuana, suggest an increase in HIV prevalence associated with drug use. Given widespread risk behaviors and rising numbers of blood borne infections among IDUs in Mexican-U.S. border cities, there is an urgent need for increased disease surveillance and culturally appropriate interventions to prevent potential epidemics of blood borne infections. We review available literature on the history of opium production in Mexico, recent trends in drug use and its implications, and the Mexican response, with special emphasis on the border cities of Ciudad Juarez and Tijuana.