This review aimed to determine longitudinal changes in objectively measured overall sedentary behaviour, and to examine their associations with adiposity in children and adolescents. A search for longitudinal studies was performed using several electronic databases. Of 161 potentially eligible papers, 10 for change in sedentary behaviour and 3 for longitudinal associations with change in adiposity were included. Weighted mean increase in daily sedentary behaviour per year was 5.7% for boys and 5.8% for girls. Only one paper included preschool children, and it showed a decrease in sedentary behaviour. Nine studies were from Western countries. Null associations were reported between sedentary behaviour and adiposity in two studies, the other found that increases in sedentary behaviour were associated with increases in adiposity, but only in those with body mass index above the 50th percentile. There was consistent evidence that sedentary behaviour increases with age in school-age children and adolescents, by approximately 30 min extra daily sedentary behaviour per year. There was little evidence on the influence of changes in sedentary behaviour on changes in adiposity. There is a need for more longitudinal research, for more evidence from outside the Western world, and for more studies that examine 'dose-response' associations between changes in sedentary behaviour and changes in adiposity.