Abstract Objective A 5-year nationwide mass media campaign aimed at prevention of overweight was organised from 2002 onwards. The present study evaluates the first campaign, which was aimed primarily at increasing awareness of weight gain. Design and subjects Data were collected by telephone interview in four independent cross-sectional surveys among non-obese Dutch adults aged 25–35 years (total n = 1949) for statistical analyses. Awareness of personal body-weight status, overweight-related risk perceptions, attitudes towards weight-gain prevention, motivation to prevent weight gain and self-reported body mass index (BMI) were measured in each survey. Campaign exposure was assessed in the post-intervention surveys. To identify intervention effects over time multiple linear and logistic regression analyses were used, adjusted for secular time effects and age. Results After the campaign about 65% of the respondents knew about the campaign. The campaign was associated with more positive attitudes towards the prevention of weight gain ( β = 0.16; P ≤ 0.01) and higher self-reported BMI ( β = 0.14; P ≤ 0.01). Conclusions The results suggest that the first campaign reached a large proportion of the population and initiated some positive change in attitudes, but did not achieve significant improvements in other determinants of weight-gain prevention among non-obese young adults.