Childhood obesity and physical inactivity (PI) are serious public health concerns of the twenty-first century. Increased prevalence of obesity and PI contribute to the high morbidity and mortality rates across the globe and have become an extra burden for low-to middle-income countries which are also under the threat of communicable- and poverty-related diseases such as malaria, malnutrition, cholera and infant mortality. It is widely documented that obesity and other metabolic risk factors of cardiovascular diseases (CVDs) in childhood are likely to persist into adulthood. However, there is limited literature on the longitudinal relationship between changes in body composition, physical activity (PA) and metabolic risk factors in relation to television (TV) watching time in children and adolescents in the Tlokwe municipality in the North-West Province of South Africa. Three manuscripts were compiled from this study. The sample of the study included two hundred and eighty-nine (289) adolescent learners (116 boys and 173 girls) from six out of eight schools that agreed to participate in the study. Out of the six schools, two were from areas around the central business district (CBD) comprising mostly adolescents from families of high socio-economic status, and four schools from township areas comprising adolescents from families of lower socio-economic status. Selected learners with a mean age of 14.9±0.76 years in 2011 (at baseline measurement), 15.6±0.77 years in 2012 and 16.4±0.78 years in 2013 participated in the study. School records, as well as participants’ birth clinic cards, were used to establish the age of the study participants. Body composition was measured according to the International Society for the Advancement of Kinanthropometry (ISAK) standard procedures. PA level was measured using the International Physical Activity Questionnaire (IPAQ). Abdominal obesity was determined using waist circumference (WC) measurements, and blood pressure (BP) was determined by Omron MIT Elite Plus, while TV watching time was determined through self-reports. The first manuscript examined the two-year longitudinal changes in body composition, PA and selected metabolic risk factors (abdominal obesity and blood pressure) in adolescents aged 14- to 16-years old. Significant mean changes were found for stature, body mass index (BMI), body mass, systolic- (SBP) and diastolic blood pressure (DBP) over the measurements period (p<0.05), with girls having consistently greater BMI, the sum of skinfolds and percentage of body fat compared to the boys. Overweight gradually increased by 7.6% (from 12.8% in 2011 to 20.4% in 2013) for the group with more girls (12.2%) being overweight than boys (2.2%), (p<0.01). Participation in low physical activity (LPA) increased by 8.2% for the whole group while moderate physical activity (MPA) gradually decreased (15.2%). With regard to the metabolic risk factors, boys had significantly higher WC (p≤0.001) compared to girls. The second manuscript examined the relationship between two-year longitudinal changes in body composition, PA and TV watching among adolescents in adolescents aged 14- to 16-years old. The partial correlation coefficient showed no significant relationship between changes in body composition, PA and TV watching time. However, changes in TV watching time and BMI were both negatively related to changes in MPA and vigorous physical activity (VPA) although the relationship was not statistically significant. After adjusting for age, the regression coefficient indicated a significant negative relationship between BMI and total physical activity (TPA) among the boys (p=0.02), and …