Patient portals facilitate patients' access to their electronic health care records, and may also include features such as patient-clinician messaging, prescription renewal, and educational resources. There is evidence that portals support patient empowerment, therapeutic communication, adherence to treatment, and satisfaction with care. Nonetheless, patient portals are underutilized in mental health settings, with policies in some health care organizations restricting all access to mental health records through patient portals. A qualitative evidence synthesis was conducted to explore the perspectives of clinicians and patients on portal use in the mental health care context represented in the current literature. A systematic search of relevant databases, followed by citation and article screening, yielded 24 qualitative and mixed-methods studies for inclusion, and a thematic synthesis was performed. The synthesis yielded five themes: impacts to the efficiency of mental health care delivery; effects on therapeutic relationships between clinicians and patients; changes to the patient-clinician power balance; the suitability of patient portals for patients with mental illness; and the complexities of information management in mental health care. Ultimately, both clinicians and patients acknowledged numerous potential benefits of patient portals, but there were also concerns about their use specific to the mental health context. These concerns were voiced primarily by clinicians, and originated in part from concern for patient safety, but also from stigmatizing attitudes and the perceived threats of portals to clinicians' workloads and control over the record. This systematic review of qualitative studies highlights opportunities for organizations to support their clinicians through the implementation of recovery-oriented initiatives like patient portals, and to support patients with mental illness by ending discriminatory policies limiting access to their records.