Background/objectives Dairy products and specifically calcium have been suggested to play a role in obesity development but more longitudinal evidence is still needed. The objective of this study was to assess the association between dairy products and total calcium intake at age 13 and body mass index at age 21. Subjects/methods This longitudinal study included 2159 individuals from the Epidemiological Health Investigation of Teenagers cohort (EPITeen), Porto, Portugal, evaluated at ages 13 and 21. Assessment consisted of anthropometrics measurements and structured questionnaires namely a semi-quantitative food frequency questionnaire to appraise food consumption in the past 12 months. Linear regression models were run in 941 individuals with complete information of confounders: gender, follow-up period, parents' education, physical activity, energy, and total calcium intake. Results Negative association was found on total calcium intake at age 13 with BMI at age 21 (model 0: β = −0.059 (95% CI: −0.113, −0.004) and model 1: −0.057 (95% CI: −0.113, −0.002)), however, no statistically significant association was found when adjusting for energy intake (model 2: β = −0.031 (95% CI: −0.110, 0.047). There were no associations between milk, yogurt, and cheese consumption at age 13 and BMI at age 21 when adjusting for confounders. Conclusions This study did not support an independent effect of dairy products or total calcium intake in adolescence on later early adulthood adiposity.