Unique challenges surface when providing services in community mental health centers for persons with mental retardation and mental illness. Before any type of mental health treatment for a client with this dual diagnosis can begin, proper assessment is critical. Clinicians working with this population have to adapt their treatment strategies and assessments to the cognitive level of their clients. In addition, persons with mental retardation rarely seek out treatment on their own. Using a personal psychotherapy/counseling perspective, counselors need to carefully build relationship components which include the essential attributes of genuiness, empathy, and unconditional positive regard. In addition to a strong therapeutic relationship, the counseling environment must be seen as supportive, beginning with the initial interview. Key factors include setting a positive emotional tone for interactions, responsive and active listening, labeling feelings, and interpreting in understandable ways the client's statements and feelings expressed. The highly verbal nature of the counseling process is an important factor to consider when working with clients who may have limited or no verbal abilities due to their level of cognitive impairment. Specific types of therapies are examined. Education for mental health service providers treating these clients is strongly recommended. Contains 22 references. (JBJ)