Background: People living in residential aged care homes are entitled to a safe environment 24 hours a day, 7 days a week. Unfortunately, past evidence tells us this is not always the case and that our most vulnerable population experience high rates of adverse events. Aim: To determine whether after-hours shifts are associated with number of adverse events, independent of registered nurse staffing levels and residential aged care home size. Methods: Retrospective cohort design with multilevel modelling. Adverse events, registered nurse staffing and facility size were collected via routine reporting from ten homes (1020 beds) in one Australian state for three months in 2017. Findings: Residents records (n = 1560) of adverse events were collected from ten Residential Aged Care Homes with 1020 beds. An adverse event was reported, on average, every second shift per home. During afterhours shifts, there was an inverse association between nurse staffing and adverse events, such that lower nurse staffing was associated with higher rates of adverse events, specifically for falls and pressure injuries/skin tears. During day shifts, this effect was not seen. Discussion: The findings support statements made at the Royal Commission into Aged Care Quality and Safety regarding the lack of adequacy of nurse staffing supervision during and after hours and may contribute to considerations of upcoming mandated registered nursing contact hours for 16 of the 24 hours in a day. Conclusion: During after-hour shifts, but not day shifts, having fewer nurses is associated with more likelihood of adverse event occurrences in Australian residential aged care homes. More research, in more sites and across more organisations, with better granulation across day, evening, night and weekend/public holiday shifts will improve understanding and responsiveness to the phenomena. Future research examining falls should include staffing levels.