No systematic comparison has been conducted in Fiji using all suitable surveys of type 2 diabetes mellitus (T2DM) and obesity prevalence after standardizing methodology and definitions.Unit records from six surveys of Fiji adults were variously adjusted for age, ethnicity (Fiji Melanesians, i-Taukei, and Fijians of Asian Indian descent [Indians]) and urban-rural by sex to previous censuses. Trends were assessed using meta-regression (random effect models) and estimates projected to 2020. Poisson regression of strata was used to assess the effect of body mass index (BMI) increases on T2DM period trends.Over 1980-2011, T2DM prevalence increased in i-Taukei men (3.2% to 11.1%; 1.32%/5 years) and women (5.3% to 13.6%; 1.40%/5 years) and Indian men (11.1% to 17.9%; 1.24%/5 years) and women (11.2% to 19.9%; 1.71%/5 years). Projected T2DM prevalence in 2020 is 13.3% and 16.7% in i-Taukei men and women, and 23.4% and 24.1% in Indian men and women, respectively. Obesity prevalence increased in i-Taukei men (12.6% to 28.9%; 2.99%/5 years) and women (30.1% to 52.9%; 3.84%/5 years) and in Indian men (2.8% to 9.4%; 1.21%/5 years) and women (13.2% to 26.6%; 2.61%/5 years). Projected obesity prevalence in 2020 is 34.0% and 60.0% in i-Taukei and women, and 11.4% and 31.0% in Indian men and women, respectively. After age-adjustment, an estimated 27%, 25%, 16% and 18% of the T2DM period trend is attributable to BMI in i-Taukei men and women and Indian men and women, respectively.Prevalence of T2DM in Fiji is projected to continue increasing, driven by rising obesity, with consequences for premature mortality and life expectancy.