The literature on occupational health points to work pressure as a trigger of sickness absence. However, reliable, objective measures of work pressure are in short supply. This paper uses Danish day care teachers as an ideal case for analysing whether work pressure measured by the child-to-teacher ratio, that is, the number of children per teacher in an institution, affects teacher sickness absenteeism. We control for individual teacher characteristics, workplace characteristics, and family background characteristics of the children in the day care institutions. We perform estimations for two time periods, 2002–2003 and 2005–2006, by using generalized method of moments with lagged levels of the child-to-teacher ratio as instrument. Our estimation results are somewhat mixed. Generally, the results indicate that the child-to-teacher ratio is positively related to short-term sickness absence for nursery care teachers, but not for preschool teacher