Context: Little is known about substance use and treatment utilization in rural communities of the United States/Mexico border. Purpose: To compare substance use and need and desire for treatment in rural colonias and urban areas of the border. Methods: Interviews were conducted in 2002-2003 with a random sample of adults living in the lower Rio Grande Valley of Texas, adjacent to the Mexican border. The present analysis compares responses from 400 residents of rural colonias to those of 395 residents of cities and towns in the same geographic region. Findings: While the prevalence of drug use and drug-related problems was similar in both areas, binge drinking and alcohol dependence were higher in rural colonias than in urban areas and remained so after taking demographic and neighborhood variables into account. An increase in illicit drug use and substance-related problems in rural but not urban areas was seen when comparing results from this study with those of a previous survey conducted in 1996. The percentage of adults in potential need of treatment and the percentage motivated to seek it were similar in both urban and rural areas. However, colonia residents were more likely than their urban counterparts to be recent immigrants and to have lower incomes and educational attainment, factors that can increase the barriers they face in getting needed services. Conclusions: Rural areas are "catching up" with urban areas in problematic substance use. Given the potential barriers to accessing treatment services in rural areas, efforts should be focused on reaching those residents.