The aim of this work was to develop an index that evaluates the degree of adherence to existing dietary and lifestyle guidelines for primary school-aged children (Healthy Lifestyle-Diet Index (HLD-Index)) and examine its relationship with selected nutrient intake and insulin resistance (IR).Ten components were used to develop the HLD-Index. Scores from 0 to 4 were assigned to all components. The HLD-Index total score ranged between 0 and 40. A sample of 729 schoolchildren from Greece aged 10-12 years (The Healthy Growth Study) was used to evaluate the validation of the proposed index.The overall mean±standard deviation of the HLD-Index score was 20±4.4. Higher HLD-Index scores were associated with lower proportion of children having intakes lower than Estimated Average Requirements by Institute of Medicine. On the basis of the cutoff point of 3.16 for homeostasis model assessment of IR, 20.9% of participants were found to be insulin resistant. After adjusting for potential confounders, logistic regression showed that a 1 unit increase in the score is associated with almost 8% lower odds for being insulin resistant. The cutoff point analysis revealed that score equal to or lower than 21 best discriminates children with IR from those without IR. On the basis of this cutoff point, the sensitivity of the HLD-Index was 70% and the corresponding specificity was 47%.The proposed HLD-Index could be used by public health policy makers and other health-care professionals to identify subgroups in the population with poor diet-lifestyle habits who are at increased probability for IR.