OBJECTIVE: The purpose of this study was to assess the associations and impact of increased meal frequency, physical activity and 'skipping' breakfast on obesity levels in a sample of urban adolescents, aged 13-17 years old, from Porto, Portugal. METHODS: Overweight and obesity were defined according to age- and sex-specific BMI cut-points. Daily meal frequency was assessed by questionnaire. Self-reported physical activity was recalled. Results: The proportion of overweight/obese girls (p < or = 0.05) and boys (p < or = 0.001) that consumed fewer than three meals was significantly higher than those reported from normal-weight counterparts. While no statistically significant differences were reported in girls, obese boys skipped breakfast significantly more (13% vs 5.6%; p < or = 0.05) than normal-weight counterparts did. Normal-weight boys but not girls were significantly more active (p < or = 0.01) than obese peers. An additional meal in boys (OR: 2.75; p < or = 0.05) and girls (OR: 1.97; p < or = 0.05) reduced the risk of being overweight/obese. Regardless of gender, breakfast skipping is not seen as a predictor of being overweight/obese. However, boys (OR: 2.10; p < 0.003), but not girls, who were moderately active were more likely to be of normal weight. CONCLUSION: The data indicate that increased meal frequency may have a beneficial effect on a reduced BMI. Physical activity and breakfast skipping may be candidate targets for prevention programmes aimed at reducing overweight/obesity among adolescents.