AbstractObjectives:To examine whether high relative weight increases the risk of future sickness absence and to what extent any differences in short and long absence periods can be explained by specific obesity‐related disorders, general health, and working conditions.Research Methods and Procedures:The study included 5386 female and 1452 male employees of the city of Helsinki surveyed in 2000 to 2002. Survey data were linked to sickness absence records until the end of 2004 (mean follow‐up time 2.9 years).Results:Women and men with higher relative weight had clearly more short (1 to 3 days) and long (>3 days) periods of sickness absence during follow‐up. The associations were rather monotonic and stronger for long periods. In women, adjusting for arthrosis and gout decreased the excess risk of long periods among those who were obese. In men, arthrosis, gout, and metabolic disease explained some of the excess risk for both short and long periods among the obese. Adjusting for physical functioning and self‐rated health decreased the excess risk for short and long periods of sickness absence among obese women and men. Working conditions had almost no effect on the association between BMI and short or long periods of sickness absence.Discussion:Obesity increases the risk of having short and long periods of sickness absence. This finding can be partly explained by measures of general health and specific obesity‐related disorders. Healthy weight maintenance is a crucial issue in promoting occupational functioning and minimizing the costs associated with sickness absence.