There is growing interest in applying the multimorbidity model for mental health disorders - i.e. the interactive effects of co-occurring diagnoses. Alcohol use disorder (AUD) and tobacco use disorder (TUD) often occur together, but distinctive correlates of their co-occurrence have not been studied. Veterans treated by the Veterans Health Administration (VHA) nationally in FY 2012 with diagnoses of both AUD and TUD were compared to those with only AUD or only TUD on socio-environmental factors, medical and psychiatric diagnoses, and service use. Multimorbid effects were defined as those in which patients with both AUD and TUD had more serious problems greater likelihood of specific co-occurring conditions than those with either AUD alone or TUD alone. Veterans with concurrent AUD and TUD (N=153,397), as compared to those with AUD only (N=191,900) or with TUD only (N=643,377), had significantly higher rates of homelessness [odd ratios (ORs)=1.24, 1.68], hepatic disease (ORs=1.11, 2.18), substance use disorders (ORs=1.42, 3.14), receipt of a VA disability pension (ORs=1.26, 1.30) and use of substance and mental health outpatient services (ORs=1.04, 1.12). Veterans with AUD and TUD appear to have more severe problems in some, but not all, socio-environmental, medical, psychiatric, and service use domains than veterans with either of these diagnoses alone. The combination of AUD and TUD yield generally more adverse effects in diverse areas and thus reflect an emergent phenomenon that may a require a distinctive treatment approach.