Youth with mental retardation* (MR) have experienced increasing levels of participation in community life over the last 30 years. This freedom has facilitated access to community life beyond school settings; it has also created the potential for alcohol and drug use and for the development of substance abuse (SA). Little is known about access to SA treatment for youth with MR—an especially vulnerable population. Through the application of a set of standardized performance measures, this study examines SA treatment access among youth aged 12 to 21 with and without MR (N = 150,009). Guided by Andersen’s sociobehavioral model of health care utilization, multivariate logistic regression analyses modeled SA treatment initiation and engagement. Youth with MR and SA were less likely to initiate or engage in treatment. Engagement among youth with MR and SA was associated with being male and/or non-White. Implications relate to a need for improved treatment access for youth with MR and SA through cross-system collaboration.