Ethnicity is a consistent correlate of excess weight in youth. We examine the influence of lifestyles on ethnic differences in excess weight in early adolescence in the UK. Data were collected from 6599 pupils, aged 11-13 years in 51 schools, on dietary practices and physical activity, parental smoking and overweight, and on overweight and obesity (using International Obesity Task Force criteria). Skipping breakfast [girls odds ratio (OR) 1.74, 95% confidence interval (CI) 1.30-2.34; boys OR 2.06; CI 1.57-2.70], maternal smoking (girls OR 2.04, CI 1.49-2.79; boys OR 1.63, CI 1.21-2.21) and maternal overweight (girls OR 2.01, CI 1.29-3.13; boys OR 2.47, CI 1.63-3.73) were associated with obesity. Skipping breakfast, more common among girls, was associated with other poor dietary practices. Compared with White UK peers, Black Caribbeans (girls OR 1.62, CI 1.24-2.12; boys OR 1.49, CI 1.15-1.95) and Black Africans (girls OR 1.96, CI 1.52-2.53; boys OR 2.50, CI 1.92-3.27) were more likely to skip breakfast and engage in other poor dietary practices, and Indians were least likely. White Other boys reported more maternal smoking (OR 1.37, CI 1.03-1.82). All these reports were more common among those born in the UK than those born elsewhere. Black Caribbean girls were more likely to be overweight (OR 1.38, CI 1.02-1.87) and obese (OR 1.65, CI 1.05-2.58), Black African girls to be overweight (OR 1.35, CI 1.02-1.79) and White Other boys to be overweight (OR 1.37, CI 1.00-1.88) and obese (OR 1.86, CI 1.15-3.00). Adverse dietary habits and being born in the UK contributed to these patterns. These findings signal a potential exacerbating effect on ethnic differences in obesity if adverse dietary habits persist. Combined adolescent and parent-focused interventions should be considered.