A nationwide representative survey of New Zealand schoolchildren showed a 2.7% incidence of extreme obesity (versus 4% in the United States) but revealed worrying ethnic differences in prevalence. Prevalence percentages (95% CI) were 0.8 (0.4 to 1.9), 5.1 (3.6 to 7.1), and 10.9 (8.9 to 13.3) in New Zealand European, Māori, and Pacific Island groups, respectively. These findings warrant remedial action.