To investigate whether the secular trend in the increasing prevalence of overweight and obesity among 16- to 20-year-old adolescents in Iceland varied by levels of parental education and family structure. Odds ratios were calculated from repeated population-based, cross-sectional surveys comprising cohorts of 16- to 20-year-old Icelandic adolescents attending junior colleges in 1992 (n=4,922), 2004 (n=11,031), 2007 (n=11,229), and 2010 (n=11,388). Body mass index (BMI) was calculated from self-reported weight and height and categorised as normal weight or overweight and obese, and examined in relation to parental education level and family structure. The odds of being overweight increased by 2.62 and 1.71 for boys and girls respectively over each of the survey time points. The prevalence of overweight and obesity increased across all three subgroups (low, medium, and high) of parental education level. The probability of overweight across all years were consistently the highest for youths with parents in the low-education category followed by middle-educated and high-educated parental background (p<0.05). The gap in overweight and obesity trends between respondents' parental education backgrounds increased over time and was generally explained more by the fathers' education than by the mothers' education (p<0.05). Family structure was not associated with the prevalence of overweight and obesity in our data. Differences in parental levels of education are associated with accelerating trends in prevalence of overweight and obesity among 16- to 20-year-old adolescents in Iceland.