The purpose of this study was to investigate the associations between chest circumference in infancy and rapid growth or obesity at 3 years of age. We conducted a retrospective observational study of 1353 children in Kumamoto, Japan. Data collected included chest circumference, head circumference, weight, and body mass index. The area under the receiver operating characteristic curves for chest circumference were analyzed to determine the ability of this index to identify obesity at 3 years of age. Chest circumference at 3-4 months of age and increases in chest circumference during the first 3-4 months of life had higher mean standard deviation scores for rapid growth than for slow or no change in growth (p<0.05). Chest circumference and the increase in chest circumference were also positively correlated with rapid weight gain, and were associated with obesity at 3 years of age. The area under the curve for chest circumference was significantly different from the area under the curve for weight z-score at 6-9 months but not for weight z-score at 3-4 months. In conclusion, we found that chest circumference is associated with obesity in young children, and is positively correlated with rapid growth. Therefore, chest circumference may be a useful marker for rapid growth, and may help clinicians to identify obese children at 3 years of age.