32The aim of this study was to identify the levels of physical activity and sedentary 33 behaviour of children and adolescents with sickle cell disease (SCA) compared 34 to healthy individuals. A cross-sectional study with a quantitative approach was 35 performed at a reference center for the treatment of patients with 36 hemoglobinopathies in northeastern Brazil. Patients were recruited between 37 October 2015 and January 2017. Eligible participants answered a Physical 38 Activity Questionnaire for Older Children and Adolescents (PAQ-C) and were 39 instructed to use an ActiGraph wGT3X-BT triaxial accelerometer for seven 40 consecutive days. The analysis of the results was performed using the SPSS 41 software (version 13.0). Differences between means were analysed using the 42 Mann-Whitney U test and the chi-square test was used to evaluate the 43 proportions of occurrence of categorical variables, comparing patient and 44 controls groups. Among the 352 patients in the follow-up, 64 met the inclusion 45 criteria and agreed to participate. Of those, 14 did not use the accelerometer 46 during the 7 consecutive days and were excluded. 50 patients (and their 50 47 controls) were then evaluated. We observed a statistically significant difference 48 between cases and controls in the variables "total time of moderate and vigorous 49 physical activity" (p=0.009 and p=0.0001, respectively) and "daily mean of 50 moderate and vigorous physical activity" (p=0.005 and p=0.003). There was also 51 a significant difference among cases and controls in the following variables: 52 "metabolic equivalent" (MET), with p=0.04, total of steps (p=0.04) and "total 53 caloric expenditure" (p=0.0001), with the worst performances for the group of 54 patients with SCA. Children and adolescents with SCA presented lower levels of 55 physical activity than healthy children and adolescents, both when evaluated by 3 56 the PAQs or by the accelerometer. The results suggest the need to develop 57 specific programs aimed at promoting physical activity levels and reducing 58 sedentary behaviour among young individuals with SCA. 59 Sickle cell anemia is a hereditary and hematological disease that occurs due to 63 the abnormal production of red blood cells. On the other hand, childhood physical 64 activity has beneficial effects on health, both in the short and long terms, and may 65 reduce risk factors for chronic diseases. The aim of this study was to identify the 66 levels of physical activity and sedentary behaviour of children and adolescents 67 with sickle cell disease compared to healthy individuals. Participants answered a 68 Physical Activity Questionnaire for Older Children and Adolescents (PAQ-C) and 69 were instructed to use an ActiGraph wGT3X-BT triaxial accelerometer for seven 70 consecutive days. We observed children and adolescents with sickle cell anemia 71 presented lower levels of physical activity than healthy children and adolescents, 72 both when evaluated by the PAQs or by the accelerometer. The results suggest 73 the nee...