Objectives. To evaluate the trajectories of change in obesity within and between Tehranian families, who participated in the Tehran Lipid and Glucose Study (TLGS). Methods. This study is a family-based longitudinal design, in four waves. A total of 14761 individuals, within 3980 families, were selected. Three anthropometric measurements, body mass index (BMI), waist circumference (WC), and a body shape index (ABSI), were recorded. Multilevel latent growth curve modeling (MLGCM) approach was used for evaluating the change trajectories in obesity within and between the families. Results. The mean age of the subjects in the present study was 33.28 ± 19.01 (range 3-89 years) and 50.1% were male. Obesity was significantly increased (P < 0.001). Individuals with more fat become obese slower, whereas families with more fat become obese faster (P < 0.001). The initial value and growth rate of WC and ABSI were greater in men than in women, while this result is contrary to BMI (P < 0.001). Conclusions. Our findings demonstrated that there is an alarming increase in the obesity trend in Tehranian families. The important role of the family in the prevention of obesity is highlighted, underlining the need for public health programs, as family centered educations to lifestyle modification, which can address this emerging crisis.