The objective of the current study is to examine changes in body mass index (BMI) and waist circumference among New Zealand adolescents between 1997/1998 and 2005. Data were drawn from two cross-sectional studies of high school students in an economically disadvantaged region of Auckland. In total, 608 adolescents from the 1998 survey and 897 adolescents from the 2005 survey participated. The prevalence of obesity increased from 19.4% in 1997/1998 to 30.7% in 2005. The mean BMI among adolescents significantly increased from 25.3 in 1997/1998 to 27.2 in 2005, with the greatest increases at the high end of the distribution. Increases in BMI did not differ by age, gender or ethnicity. The mean waist circumference increased from 76.2 cm in 1997/1998 to 89.4 cm in 2005, with increases in waist circumference measurements at all points in the distribution. The prevalence of obesity is increasing rapidly in this sample of ethnically diverse adolescents. Corresponding increases in waist circumference measurements suggest that this population of New Zealand adolescents are at increased risk for related chronic conditions.