Background: In response to increasing policy action and public concern about the negative health effects of sugar-sweetened beverages (SSBs), there is increased promotion of artificially sweetened beverages (ASBs). These have been linked with obesity and diabetes in recent experimental work. This study examined associations between SSB and ASB consumption and changes in adiposity in a nationally representative sample of UK children. Methods: We conducted a longitudinal study of 13,170 children aged 7–11 years in the UK Millennium Cohort Study, collected in 2008 and 2012. Logistic regression was used to assess socio-demographic and behavioural correlates of weekly SSB and ASB consumption at 11 years. Linear regression examined associations between SSB/ASB consumption and changes in adiposity measures between 7 and 11 years. Results: Boys were more likely to consume SSBs weekly (62.3 % v 59.1 %) than girls at age 11 years. South Asian children were more likely to consume SSBs weekly (78.8 % v 58.4 %) but less likely to consume ASBsweekly (51.7 % v 66.3 %) than White children. Daily SSB consumption was associated with increases in percentage body fat between ages 7 and 11 (+0.57 %, 95 % confidence intervals 0.30;0.83). Daily ASB consumption was associated with increased percentage body fat at age 11 (+1.18 kg/m 2 , 0.81;1.54) and greater increases between ages 7 and 11 (+0.35 kg/m 2 , 0.09;0.61). Conclusion: Consumption of SSBs and ASBs was associated with BMI and percentage body fat increases in UK children. Obesity prevention strategies which encourage the substitution of SSBs with ASBs may not yield the adiposity benefits originally intended and this area should be a focus for further research.