BACKGROUND Few studies have addressed the influence of dietary patterns (DP) during adolescence on the amount of body fat in early adulthood. OBJECTIVE To analyze the associations between DP tracking and changes in the period between 15 and 18 years of age and the percentage of body fat (%BF) at age 18 years. METHODS We used data from 3,823 members of the 1993 Pelotas (Brazil) birth cohort. Body density was measured at age 18 years by air displacement plethysmograph (BOD POD) and the %BF was calculated applying the Siri equation. Based on the estimates from the FFQ, we identified DP at ages 15 ("Varied", "Traditional", "Dieting" and "Processed meats") and 18 years ("Varied", "Traditional", "Dieting" and "Fish, fast food and alcohol"). The DP tracking was defined as the individual's adherence to the same DP at both ages. Associations were tested using multiple linear regression models stratified by sex. RESULTS The mean %BF was 25.0% (95% CI: 24.7 to 25.4), significantly greater for girls than boys (p<0.001). The adherence to any DP at age 15 years was not associated with the %BF at age 18 years. However, individuals who adhered to a "Dieting" DP at age 18 years showed greater %BF (1.30 and 1.91 percentage points in boys and girls, respectively) in comparison with those who adhered to a "Varied" DP. Boys who presented tracking of a "Dieting" DP presented greater average %BF in comparison with others DP, as well as girls who changed from the "Traditional" or "Processed meats" DP to a "Dieting" DP. CONCLUSION These results may support public health policies and strategies focused on improving dietary habits of adolescents and young adults and preventing accumulation of body fat, especially among the adolescents with restrictive dietary habits.