ObjectiveTo describe biological and psychosocial factors associated with body mass index (BMI) for age in adolescents attending an outpatient department at Weskoppies Psychiatric Hospital.MethodsA total of 50 adolescents participated in a convenience sampling research study. BMIs were calculated using their weights and heights to distinguish different weight categories based on the 2007 World Health Organization (WHO) growth charts. Based on their BMIs, participants were categorised as underweight, normal body weight, overweight and obese. The association between the BMIs of the biological parents and their adolescent children was investigated using the Fisher’s exact test. The data collection included adolescents’ demographic information, psychiatric diagnosis, psychiatric medication, nutritional intake, eating habits and the intensity of physical activity such as sports, leisure and sedentary behaviour.SettingThe study was conducted at Weskoppies Psychiatric Hospital’s adolescents outpatient department.ResultsOf the participants, 72% were males. Forty-eight per cent of all the adolescents had a normal BMI, mostly of black African descent. When comparing the adolescents’ BMI with that of their biological mothers, 50% of those who were obese also had mothers who were mostly obese (53.8%). The Fisher’s exact test indicated a statistically significant association between the BMI categories of mothers and those of their adolescent children (Fisher’s exact test, p = 0.032). Despite the above association, no significant association could be found regarding their nutritional intake and eating habits. Also, no significant association was found between the adolescents’ BMIs and the use of psychotropic medication, as compared with other previous studies. Furthermore, no association could be found between adolescents’ BMI categories and the level of intensity of physical activity such as sports and leisure activities or sedentary behaviours.ConclusionThis study supports previous findings that a significant association exists between maternal and childhood obesity. The association between BMI and psychotropic medication, nutritional intake and eating habits, and level of physical activity could not be confirmed in our study. The study results were limited by the small sample size and the convenience sampling method. Although this was only a descriptive study, it highlighted the complexity of biological and psychosocial factors involved in weight gain. Further studies are needed to explore the interplay of physical and environmental risk factors for childhood obesity, as well as to ensure early identification and education of patients and their families to prevent development of obesity.