This paper discusses the effect of occupational hassles on negative mood and effort exertion. Expert ratings were used to measure the predictor variables, assignment complexity and hassles severity, whereas the dependent variables were measured with validated self-report scales. Using pooled-time series analysis on daily records of a sample of military jump masters (parachute trainers), it was shown that hassles severity predicted end-of-day mood, fatigue and subjective workload. This indicates that, despite their transient nature, daily hassles at work constitute a significant factor whose effect has been overlooked by available methods of occupational stress. Furthermore, the interaction between assignment complexity and hassles severity suggests that other variables, such as coping options for dealing with hassles, moderate the effect of hassles on behavioural and emotional outcomes. Since this effect can be explained by means of different theoretical constructs (i.e. effort exertion, cognitive appraisal and rate of progress) this poses a challenge for future research, both theoretical and applied.