Background To analyse the validity of diabetes declarations in a health interview survey in order to evaluate the appropriateness of using health interview surveys to understand the relationship between diabetes and social groups. Methods People with self-reported diabetes are those who report to have diabetes in the health survey. People with diabetes (gold standard) are those who were identified with fasting blood glucose level $126 mg/dl or those who were treated with oral antidiabetic drugs or insulin. Independent variables were educational level, social class and gender. The authors calculated sensitivity, specificity and k coefficient. Results The majority of indicators for evaluating the adequacy of using health interviews surveys to analyse inequalities in self-reported diabetes by social groups are good. The worst indicator was sensitivity, although it did not vary according to social groups. Conclusion Health surveys are a good instrument to evaluate the social inequalities in the prevalence of diabetes.