US pharmacies tend to be located at intersections of major cross streets throughout a city, while in the case of Mexican border cities pharmacies are clustered close to US-Mexico border crossings. Presumably this is due to the volume of US clients who frequent the pharmacies. Although the precise number of border crossings to purchase medications is unclear, it is thought to be significant. In the past, patient-based surveys were the primary source for information regarding US residents crossing the border into Mexico for prescription medications. The current study examines the distribution of pharmacies throughout Ciudad Juárez, Chihuahua, Mexico, recording the change in the number of pharmacies over a 15-year period and suggesting the scale of US residents who use Mexican pharmacies. Field research was conducted in 1996 and 2011. Maps showing the location of pharmacies for these two years indicate a clustering of pharmacies within one and one-half miles of the city’s two principal border-crossings between the United States and Mexico. Provider-based surveys revealed that the majority of patients who use pharmacies closest to the border were US residents.