This study presents the results of an assessment of 377 Mexican heritage 7th grade adolescents attending middle school in Arizona. The students answered questions concerning personal substance use, linguistic acculturation and parental monitoring. Linguistic acculturation in general did not predict substance use, while greater perceived parental monitoring significantly predicted a lesser likelihood to use substances for both boys and girls. There was a significant acculturation by parental monitoring interaction for every use of alcohol for boys, with parent monitoring effects being more pronounced in reducing alcohol use among highly acculturated boys. Results are discussed in terms of how acculturation impacts family processes and the drug use behaviors of Mexican heritage adolescents living in predominantly Mexican enclaves. Abstract published by arrangement with Taylor and Francis.