Online patient portals may be effective for engaging patients with mental health conditions in their own health care. This retrospective database analysis reports patient portal use among Veterans with mental health diagnoses. Unadjusted and adjusted odds of portal feature use was calculated using logistic regressions. Having experienced military sexual trauma or having an anxiety disorder, post-traumatic stress disorder, or depression were associated with increased odds of portal use; bipolar, substance use, psychotic and adjustment disorders were associated with decreased odds. Future research should examine factors that influence portal use to understand diagnosis-level differences and improve engagement with such tools.