The purpose of this study was to determine diet quality and physical activity behaviours of grade 6 students by sex and body weight status, and to determine the associations between diet quality and physical activity behaviours. The Web-based Food Behaviour Questionnaire, which included a 24-h diet recall and the modified Physical Activity Questionnaire for Older Children (PAQ-C), was administered to a cross-section of schools (n = 405 students from 15 schools). Measured height and weight were used to calculate body mass index and weight status (Cole et al. 2000). A Canadian version of the Healthy Eating Index (HEI-C) was used to describe overall diet quality. The mean HEI-C was 69.6 (13.2) with the majority (72%) falling into the needs improvement category. The overall mean physical activity score was 3.7 out of a maximum of 5, with obese subjects being less active compared with normal weight and overweight (p