INTRODUCTION: Substance use disorders (SUD) are commonly comorbid with anxiety and depressive disorders, and are associated with poor treatment outcomes.The mechanisms underlying this association remain unclear–one possibility is that patients with anxiety/depressive disorders and SUD receive poorer treatment.Concerns have been raised about the quality of inpatient care received by patients with SUD. OBJECTIVES: To examine the quality of care received by inpatients with an anxiety or depressive disorder, comparing sub-groups with or without a comorbid SUD. METHOD: Retrospective case-note review of 3,795 patients admitted to inpatient psychiatric wards in England. Data were gathered on all acute admissions with anxiety/depressive illness over a 6 month period, for a number of measures of quality of care derived from national standards. Association of co-existing SUD with a variety of quality of care outcomes (relating to assessment, care planning, medication management, psychological therapies, discharge, crisis planning and follow-up) was investigated using multivariable regression analyses. RESULTS: 543(14.3%) patients in the study had a secondary diagnosis of a SUD. Patients with SUD were less likely to have had care plans that were developed jointly, (i.e.,with input from both patient and clinician; OR= 0.76, 95% CI [0.55,0.93], p =.034),and less likely to have had their medication reviewed either during the admission (OR = 0.83, 95% CI [0.69, 0.94], p=.030) or at follow-up after discharge (OR= 0.58, 95% CI [0.39,0.86], p=.007). Carers of patients with SUD were less likely to have been provided with information about available support services (OR= 0.79, 95% CI [0.57, 0.98], p=.047). Patients with SUD were less likely to have received adequate (at least 24 hours) notice in advance of their discharge (OR= 0.72, 95% CI [0.54,0.96], p=.033), as were their carers (OR= 0.63, 95% CI [0.41,0.85], p=.007). They were less likely to have a crisis plan in place at the point of discharge (OR= 0.85, 95% CI [0.74, 0.98], p= .044). There was also strong evidence that patients with SUD were less likely to have been referred for psychological therapy (OR= 0.69, 95% CI [0.55,0.87], p=.002).CONCLUSIONS: We found evidence of poor erquality of care for inpatients with anxiety and depressive disorders with comorbid SUD, highlighting the need for more to be done to support these patients. Discrepancies in care quality may be contributing to the poor treatment outcomes experienced by patients with SUD, and strategies to reduce this inequality are necessary to improve the wellbeing of this substantial patient group.