OBJECTIVE: This study sought to determine the impact of a formal screening program for substance use disorders among psychiatric inpatients. Both identification of these disorders and referrals to aftercare were measured. METHODS: A total of 193 patients admitted to a state psychiatric facility during a two-month period before screening was initiated were compared with 183 patients admitted during the same two months a year later when screening was in place. Patients were screened using the Chemical Use, Abuse, and Dependence Scale. Data were collected from hospital and statewide computerized files. RESULTS: Consistent with findings of previous studies, the formal screening procedure increased the identification of substance use disorders, even among those who were not screened during the screening period. However, despite heightened awareness of staff, referrals to outpatient treatment in the community after discharge did not increase. In fact, patients who did not have a comorbid substance use disorder were more frequently referred to aftercare than were dually diagnosed patients. CONCLUSIONS: Access to services for dually diagnosed patients may be limited by both staff and patient barriers. Underdiagnosis may be partly overcome by formal screening procedures, but staff bias may influence use of screening tools as well as aftercare referrals. In turn, individuals with a comorbid disorder who are not referred to aftercare may be more resistant to treatment and follow-up care. These issues must be clinically addressed by educating and sensitizing staff, as well as by administrative means.