Aim: The purpose of this study was to examine the effect of an obesogenic environment and social support for health behaviours on body mass index and body image in adolescents. Methods: This methodological and descriptive study was conducted in a city centre in Turkey. Interviews were made with the Provincial Directorate for National Education, and the schools in the city centre were divided into three regions according to socioeconomic levels; three schools were then determined among the regions by drawing lots. The data collection was performed with 270 students randomly selected from the three schools. A student information form, an obesogenic environment evaluation form, body cathexis scale, body mass index (BMI) and the Child and Adolescent Social Support Scale for Healthy Behaviours were used to collect data. Percentage distributions, correlations, chi-square tests, analyses of variance and independent samples t-tests were used in the data analysis. Results: According to the data acquired, 10.7% of adolescents in the study group were overweight and 3.0% were obese. There was a positive relationship between the obesogenic environment and BMI, and as the obesogenic environmental features of adolescents increased, the BMI increased, and the body image scores decreased. As social support for the adolescents’ health behaviours increased from their mothers, fathers, teachers, classmates, and close friends, BMI decreased and they were more likely to be satisfied satisfied with their bodies. Conclusion: Our results demonstrate that, while an obesogenic environment contributed to increased BMI in adolescents and decreased their body satisfaction, social support given for health behaviours had a positive effect on BMI and body perception.