This review identified 36 studies on the relation between obesity status and sick leave. Pooling of effect estimates was not possible due to great heterogeneity between studies regarding definition of sick leave (short-term/long-term), measure of obesity (body mass index/waist circumference/percentage body fat), definition of obesity status (World Health Organization standards/other), study population (sex/age/occupation/country) and exposure and outcome ascertainment (self-reported/objectively assessed). Nevertheless, a clear trend towards greater sick leave among obese compared with normal weight workers could be discerned, especially for spells of longer duration. In studies from the USA, which consistently reported about five times lower number of sick leave days per person-year than European, obese workers had about 1-3 extra days of absence per person-year compared with their normal weight counterparts. In European studies, the corresponding difference was about 10 d. For overweight workers the data were conflicting, indicating either increased or neutral level of sick leave compared with normal weight. Regarding underweight, the studies were very few and concerns regarding direction of causality were greater. Finally, in all four interventional studies identified substantial weight loss in obese subjects resulted in reduced sick leave, at least temporarily. In conclusion, increasing obesity in children and adults is likely to negatively affect future productivity as obesity increases the risk of sick leave, disability pension and death.