The main objective of this study is to analyse the effect of the professional environment on sick leaves. The professional context is approximated by the sector of activity. The database used - Hygie (2005-2008) - allows taking individual heterogeneity into account thanks to the longitudinal dimension. Sick leave probability is estimated through a fixed effects logit model and the duration (number of days absent due to sickness) is estimated through a fixed effects Poisson model. The results show that sectors of activity differ in sick leave duration rather than in the occurrence. Indeed, taking into account individual heterogeneity and differences in health status and wages reduces the variability in sick leave probability between sectors by half. On the other hand, the sector remains decisive in explaining sick leave durations. This residual variability may refer to unobserved differences in working conditions, in the generosity of daily sick pay benefits or in job insecurity.