Objective Nutritional interventions to decrease energy intake, aimed at portion sizes and front-of-package labelling, are effective only if people do not compensate for their reduced energy intake. Since several observational studies indicate that these interventions could prompt compensation behaviour, it is important to assess underlying beliefs. Therefore, the purpose of the two studies reported here was to develop a Diet-related Compensatory Health Beliefs Scale (Diet-CHBS). Design Cross-sectional surveys were conducted for the scale development. Study 1 provided data on the factor analysis and convergent validity, while Study 2 assessed the Diet-CHBS' test-retest reliability. Settings VU University Amsterdam (Study 1) and twenty-five worksite cafeterias in the Netherlands (Study 2). Subjects Study 1 was conducted among 179 students and their parents; Study 2 was conducted among 119 worksite cafeteria visitors. Results The results of Study 1 showed that the scale consisted of the hypothesized factors of compensation beliefs with regard to portion sizes (α = 0·73), front-of-package health logos (α = 0·77) and exercise (α = 0·75). The scale's overall Cronbach's α was 0·82. The Diet-CHBS had a Pearson correlation of 0·32 with a general health compensatory beliefs scale, signifying satisfactory convergent validity. Study 2 showed that the intra-class correlation coefficient between T1 and T2 was 0·69, indicating adequate test-retest reliability. Conclusion The Diet-CHBS is a valid and reliable instrument for assessing diet-related compensatory health beliefs in response to nutritional interventions. It is important to take such beliefs into account in further intervention studies aimed at preventing overweight and obesity. © The Authors 2012.