Objectives: Prior literature has documented the global burden of serious mental illnesses. The present study aimed to compare the sleep quality in caregivers of older patients with schizophrenia spectrum and bipolar disorders with control participants who did not serve as caregivers. Methods: We performed a case-controlled, cross-sectional study among family caregivers of older patients with psychotic disorders in Razi Hospital, Tunisia. Subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index Scale (PSQI). Results: Fifty caregivers of older patients (≥ 60 years) with schizophrenia spectrum and bipolar disorders, and 50 matched controls were enrolled. The three sub-dimensions of the PSQI, namely subjective sleep quality, sleep duration, and sleep efficiency, as well as overall PSQI scores, were worse for caregiver participants. Hierarchical multiple regression analyses predicting PSQI scores revealed that caregivers' age and marital status were the only significant predictors in the final model. Conclusions: Older adults with severe mental disorders constitute a vulnerable population which generates a significant burden of care, and impacts their caregivers' subjective sleep quality. Clinical Implications: Family interventions, including sleep interventions, should be considered as an integral component of treatment for serious mental illnesses. When promoting sleep quality, older and single caregivers should be targeted.