BackgroundSleep and mental health share a bidirectional relationship whereby problems in one exacerbate the other. Accordingly, sleep problems are frequent and severe in serious mental illness (SMI) populations, exacerbating SMI symptoms. This study examined the documentation and treatment of sleep problems within anonymised clinical records of SMI patients, and their association with attendance rates and number of appointments scheduled. MethodsPatient records between 01.09.2021 and 31.08.2022 were identified and relevant records (n = 229) extracted from an NHS Trust database. Content analysis was used to assess documentation and treatment of sleep problems and Chi-square tests were used to assess demographic differences. Mann-Whitney U tests were used to compare attendance rates and number of appointments scheduled between patients with/without sleep problems. ResultsMost (n = 170; 84 %) patients with sleep problems had no or minimal assessment of the sleep problem within their records. Patients were primarily offered no (n = 115; 57 %) or non-recommended (n = 69; 34 %) sleep treatment. More outpatients were offered no sleep treatment (n = 89; 64 %) than inpatients (n = 26; 41 %) (p = .002) whilst more inpatients were offered non-recommended sleep treatments (n = 33; 52 %) than outpatients (n = 36; 26 %) (p < .001). No significant associations were found between sleep and attendance or appointments scheduled. ConclusionsThere is a lack of routine clinical attention to sleep assessment and treatment in SMI groups. Where sleep is addressed, treatment often conflicts with guidelines. Improved sleep assessment and treatment could significantly enhance current SMI patient care.