Relapse/repeated episodes are defined as the admission of a child with a diagnosis of severe acute malnutrition (SAM) after being discharged with a status of recovery. However, there is a lack of study that documented the time to relapse of SAM and its risk factors. The present study aimed to identify the time of relapse and its risk factor among under-five children discharged after undergoing treatment for SAM in health facilities of Hadiya Zone, South Ethiopia. An institution-based retrospective cohort study was carried out in the Hadiya Zone of Southern Ethiopia among under-five children. Data were collected from 760 cards of severe acute malnourished children over the past 5 years spanning from 2014/15 to 2019/20. Both first admission and relapse data were abstracted from the records of the SAM children from 1 August to 30 August 2020 and cards of children that were admitted to program by transferee with complete records were included. After checking all the assumptions, multivariable Cox Proportional Hazards model was fitted to isolate independent determinants of time to cure. All tests were two-sided and statistical significance at P-values < 0⋅05. The mean(±sd) time for relapse of SAM among under-five children was 22(±9⋅9) weeks from discharge to relapse time. On multivariable Cox Proportional Hazards model, the hazard of relapse for SAM was significantly higher for children who had oedema (AHR 2⋅02, 95 % CI 1⋅17, 3⋅50), age of 6–11 months (AHR 5⋅2, 95 % CI 1⋅95, 13⋅87) had discharge MUAC not cured (AHR12, 95% CI 7⋅90, 19⋅52). The finding showed that children discharged from SAM are likely to have relapse in 3 weeks time.