Objective: Little research has addressed the relationships among infant temperament, eating styles and obesity risk. To address this gap, we tested whether infant temperament and eating patterns at the age of 1 year are associated with a greater increase in standardized weight status, and greater obesity risk at 6 years of age. Design: A secondary, prospective analysis of the Colorado Adoption Study was conducted. The main predictor variables were infant temperament (that is, emotionality, activity, attention span-persistence, reaction to food and soothability) and eating domains (that is, reactivity to food, predictable appetite and distractability at mealtime) at the age of 1 year, along with the body mass index (BMI) of biological mothers. The outcome measures were child weight and height (length) assessed at ages 1 through 6 years, from which weight-for-length and BMI were computed along with the standardized indexes (z-scores) and percentiles. Overweight/obesity status was computed at each year as well. Participants: A primarily White sample of 262 boys and 225 girls, assessed at ages 1 through 6 years, along with their mothers. Results: Among boys, greater attention span-persistence was associated with reduced standardized weight status gain (b ¼ À0.15, Po0.05) and reduced obesity risk (odds ratio (OR) ¼ 0.46, P ¼ 0.06). Among girls, greater soothability and negative reaction to food were associated with greater standardized weight status gain (b ¼ 0.19, Po0.01; and b ¼ 0.16, Po0.05, respectively) and increased obesity risk (OR ¼ 3.72, P ¼ 0.03; and OR ¼ 2.81, P ¼ 0.08, respectively). Biological mothers' obesity status predicted obesity risk in boys (OR ¼ 3.07, P ¼ 0.01) and girls (OR ¼ 5.94, P ¼ 0.03). Conclusions: Male infants with less attention span, and female infants with greater soothability or a more negative food reaction, showed greater increases in standardized weight and were more likely to be overweight/obese at the age of 6 years. The role of infant temperament in pediatric obesity onset warrants greater research.