This study aimed to assess whether weight, length, and conditional growth during the first year are associated with glycemia and insulin resistance among young adults. A non-concurrent longitudinal design was used in the study. This is a population-based cohort study, composed of people aged from 22 to 28 years. We estimated z-scores from birth to the first year and the infants were classified as stunted, underweight, overweight, obese, wasted, and at risk of wasting, using cut-offs proposed by the World Health Organization (Child Growth Standards, 2006). Conditional weight and length gain variables were estimated. Glycemia, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), and single point insulin sensitivity estimator (SPISE) were evaluated in adulthood. Multiple linear regressions that includes the variables associated with glycemia and insulin resistance were used. In total, 1,070 subjects were evaluated and glycemia in adulthood was higher among subjects who were wasted or at risk of wasting at 12 months (β coefficient = 2.77; 95%CI: 0.37; 5.21). In relation to normal weight, those subjects who were overweight at 12 months showed the lowest glycemia (β coefficient = -2.39; 95%CI: -4.32; -0.36). Conditional weight gain in the first year was negatively associated with glycemia in adulthood (β coefficient = -0.65; 95%CI: -1.23; -0.08). SPISE was higher among underweight subjects, and negatively associated with conditional relative weight gain and conditional linear growth in the first year. In conclusion, we found that undernutrition and suboptimal growth were associated with higher glycemia.