This paper examined the influence of sickness presenteeism, defined here as going to work despite illness, and sickness absenteeism behaviour on employee psychological wellbeing, work performance and perceived organizational commitment in a sample of UK workers (n=552). Self-report measures were administered on two occasions, separated by one year, to employees from four public sector and two private sector organizations. Structural Equation Modelling (SEM) was used to evaluate simultaneous influences of sickness presenteeism and sickness absenteeism on outcomes over time. Results suggested that employees reporting sickness presenteeism reported lower work performance in comparison to those reporting no sickness presenteeism, when measured concurrently but not over time. Employees reporting any sickness presenteeism in the previous three months showed relatively reduced psychological wellbeing but there was no significant association over time. Six or more days sickness presenteeism was associated with a reduction in employee perceptions that their organization was committed to them, concurrently and over time. There were no significant influences of sickness absenteeism on any outcome measure. Our results strengthen previous research and suggest that sickness presenteeism, but not sickness absenteeism, has implications for individual outcomes. The findings have implications for the way organizations manage their sickness absence systems.