Evidence from longitudinal studies on the association between diet quality and change in anthropometric measures is scarce. We therefore investigated the relationship between a recently developed food-based dietary index and change in measured BMI and waist circumference (WC) in Australian adults (1992–2007). We used data from the Australian population-based Nambour Skin Cancer Study comprising 1231 adults aged 25–75 years at baseline (1992). We applied generalised estimating equations (GEE) to examine the association between diet quality and change in anthropometric measures. Dietary intake was assessed by an FFQ in 1992, 1996 and 2007. Diet quality was estimated using the dietary guideline index (DGI), developed to reflect the dietary guidelines for Australian adults; a higher score indicating increased compliance. Multivariable models, stratified by sex, were adjusted for sociodemographic and lifestyle characteristics. We show that men with higher diet quality had a lower gain in BMI as compared to those with low diet quality during the 15-year follow-up. In a multivariable adjusted model, as compared to men in quartile 1 (reference), those in the highest quartile had the lowest gain in BMI (mean (95 % CI): 0·05 (0·00, 0·09) v. 0·11 (0·06, 0·16) kg/m2 per year, P =0·01). Diet quality was inversely, but non-significantly associated with change in WC. In women, DGI score was unrelated to change in any body measure. Energy underreporting did not explain the lack of association. We conclude that adherence to a high-quality diet according to Australian dietary guidelines leads to lower gain in BMI and WC in middle-aged men, but not in women.