PURPOSE: to investigate the myofunctional and electromyographic characteristics of obese patients in relation to sex and age group. METHOD: a convenience sample of 28 obese children and adolescents of both sexes, participants in the group of the Obesity Clinic of Pediatrics, University Hospital of Santa Maria, in the period of January to July 2011. The myofunctional characteristics were performed by experienced speech pathologist through the Assessment Protocol Myofunctional with scores (AMIOFE). Electromyographic evaluation of masseter and temporal muscles was obtained using the Lynx Electromyograph and were held three collections for each of the situations (rest, chewing, swallowing and maximum intercuspation). The EMG data were normalized, expressed as a percentage, using the mean of maximal intercuspation of each muscle studied in the assessments. RESULTS: most of the obese in this research presented myofunctional characteristics within the normal range, not being statistically significant difference when compared by sex and age. Although the average standard of the electrical activity of masseter and temporal muscles during rest, chewing and swallowing obese according to sex and age showed no statistically significant difference, there is an increased activation of the masseter muscles than the temporal. CONCLUSIONS: it can be concluded that obese children and adolescents of both sexes have myofunctional characteristics within normal limits and there is an increased activation of the masseter muscles for chewing and swallowing of the temporal muscles.