Unplanned absenteeism (UA), which includes medically certified leave (MC) or emergency leave (EL), among nurses may disturb the work performance of their team and disrupt the quality of patient care. Currently, there is limited study in Malaysia that examines the role of stressors in determining absenteeism among nurses. Therefore, apart from estimating the prevalence and the reasons of UA among nurses in Malaysia, this study aims to determine its stressor-related determinants. A cross-sectional study was conducted among 697 randomly sampled nurses working in Selangor, Malaysia. Most of them were female (97.3%), married (83.4%), and working in shifts (64.4%) in hospital settings (64.3%). In the past year, the prevalence of ever taking MC and EL were 49.1% and 48.4%, respectively. The mean frequency of MC and EL were 1.80 (SD = 1.593) and 1.92 (SD = 1.272) times, respectively. Meanwhile, the mean duration of MC and EL were 4.24 (SD = 10.355) and 2.39 (SD = 1.966) days, respectively. The most common reason for MC and EL was unspecified fever (39.2%) and child sickness (51.9%), respectively. The stressor-related determinants of durations of MC were inadequate preparation at the workplace (Adj.b = −1.065) and conflict with doctors (adjusted regression coefficient (Adj.b) = 0.491). On the other hand, the stressor-related determinants of durations of EL were conflict with spouse (Adj.b = 0.536), sexual conflict (Adj.b = −0.435), no babysitter (Adj.b = 0.440), inadequate preparation at workplace (Adj.b = 0.257), lack of staff support (Adj.b = −0.190) and conflict with doctors (Adj.b = −0.112). The stressor-related determinants of the frequency of MC were conflicts over household tasks (Adj.b = −0.261), no time with family (Adj.b = 0.257), dangerous surroundings (Adj.b = 0.734), conflict with close friends (Adj.b = −0.467), and death and dying (Adj.b = 0.051). In contrast, the stressor-related determinants of frequency of EL were not enough money (Adj.b = −0.334), conflicts with spouse (Adj.b = 0.383), pressure from relatives (Adj.b = 0.207), and inadequate preparation (Adj.b = 0.090). In conclusion, apart from the considerably high prevalence of unplanned absenteeism and its varying frequency, duration and reasons, there is no clear distinction in the role between workplace and non-workplace stressors in determining MC or EL among nurses in Malaysia; thus, preventive measures that target both type of stressors are warranted. Future studies should consider longitudinal design and mixed-method approaches using a comprehensive model of absenteeism.