This analysis examines period trends in body weight of Australian 18-24 year olds. Secondary analysis of National Health Surveys was performed, including examination of socio-demographic determinants of obesity. The prevalence of overweight and obesity has increased from 24.0 and 5.1% in males and 13.2 and 5.8% in females, respectively, in 1995 to 29.3 and 13.8% in males and 20.6 and 20.6% in females in 2012. Mean body mass index (BMI) increased over time from 23.7 (s.d. 3.5) for males and 22.4 (s.d. 4.0) for females in 1995 to 25.2 (s.d. 4.8) and 25.5 (s.d. 5.9) in 2011/2. Lower educational attainment increased the odds of having BMI ≥ 25.00 kg/m2 for both sexes (P=0.03 males and P<0.001 females). Overweight and obesity were higher in rural females (P<0.05) and those socio-economically disadvantaged (P<0.0001). The obesity epidemic has worsened for Australian young adults and in particular young females.