Patient-reported outcome measures (PROMs) are used as part of clinical practice to determine the impact of the condition and treatment interventions on a patient's health and quality of life. The Patient Health Questionnaire-9 (PHQ-9) is a self-administered diagnostic tool that has been widely adopted for the detection and monitoring of depression. This analysis reports the change in PHQ-9 scores from admission to discharge in patients admitted for depression to a South African acute psychiatric facility and aims to quantify the treatment effect of the admission using the PHQ-9 as the measurement tool. South African acute psychiatric facility. This was a retrospective observational study of all patients admitted to Netcare Akeso acute psychiatric facilities from 01 January 2018 to 31 October 2022. Patients were included if they were ≥ 18 years of age, admitted with a primary International Classification of Disease (ICD)-10 code for depression (i.e. F32-F33) and fully completed both an admission and discharge PHQ-9 questionnaire. We excluded facilities focusing only on the treatment of patients with specialised conditions such as addiction or eating disorders. This analysis included 13 308 patients admitted for depression at 10 different facilities. The median PHQ-9 score on admission was 19 (interquartile range [IQR] 14-23) and 5 (IQR 2-11) on discharge, with a median change of -12 (IQR -5 to -18). A minimal clinically important difference was seen in 87.6% patients (n = 10 091/11 515); a treatment effect was seen in 74.5% of patients and a clinically significant improvement was seen in 72.1% of patients. With the average patient reporting a four-fold reduction in the severity of their depression scores, PROMs provide a critical patient-centred window into the benefit that an inpatient admission has on those suffering with depression. These changes are consistent with those seen internationally and provide a baseline for understanding the treatment efficacy of an inpatient admission for the treatment of depression.