Abstract Introduction People diagnosed with serious mental illnesses (SMI), including schizophrenia-spectrum disorders, bipolar disorders, and major depression with psychosis, report high rates of clinically significant sleep disturbance. Yet, examination of how demographic- and health-related factors impact diagnosis and treatment in this group is scarce. We aimed to fill this gap by examining medical records of Veterans receiving treatment in VA VISN 4 healthcare facilities. Methods We used VA health record data to examine comorbidity between SMI and sleep diagnoses and receipt of sleep treatment from 2011-2019 (total N=573,974). A combination of descriptive and statistical techniques were used to investigate prevalence of sleep disorders, receipt of sleep treatment, and associations with demographic- and health-related factors. Results In 2019, 21.8% of Veterans with SMI were diagnosed with sleep disorder(s) in the medical record. White Veterans with SMI were more likely to have a sleep disorder than Veterans identifying as racial minorities. Veterans with SMI and sleep disorders were also younger, had higher BMIs, and had more medical comorbidities. Veterans with SMI were more likely to receive sleep treatment than Veterans without SMI, primarily driven by higher rates of sleep medication. Importantly, in contrast to findings regarding sleep disorder comorbidity, Veterans identifying as racial minorities received sleep treatment at a higher rate than White Veterans, and Veterans with higher BMIs received sleep treatment at a lower rate. Demographic factors including sex, age, and rurality were also associated in varying ways with rates of sleep treatment. Conclusion Our findings suggest that Veterans with SMI are being treated for sleep disorders at higher rates than Veterans without SMI. However, diagnosis and treatment are differentially impacted by demographic and health-related factors. Work is needed to better understand drivers of demographic differences and to examine any potential inequities in diagnosis or treatment of sleep disorders in Veterans with SMI. Support (if any) This work was funded by the Veterans Health Foundation (Co-PIs: Bonfils & Longenecker). Additional support was provided by pilot project funds (PI: Bramoweth) from the Department of Veterans Affairs VISN 4 Mental Illness Research, Education and Clinical Center and the Mississippi Center for Clinical & Translational Research (U54GM115428).