OBJECTIVE: The objectives of the study were to see how much of the variation in weight-for-height z-scores (WHZ) and surface area/body mass ratio (SA/mass) were associated with regional (county) differences including mean temperature. SUBJECTS AND METHODS: Longitudinal data were obtained from routine medical check-ups on 8,373 children from nine counties across Chile. WHZ and SA/mass were calculated from weight and height from birth to 3-years old at 6 monthly intervals. County of birth was used as an independent variable after controlling for sociodemographic factors. Sequential repeated-measures ANOVAs were used to analyze the changes in WHZ and SA/mass over the seven measurements from birth to 3 years of age. Simple and partial Pearson correlations were calculated between WHZ and annual mean temperature and between SA/mass and annual mean temperature after controlling for socioeconomic factors. RESULTS: County of birth was significantly (p < 0.001) associated with both WHZ and SA/mass. There was a progressive decrease in WHZ means and a progressive increase in SA/mass means from colder to warmer counties. Significant negative correlation in WHZ (r < -0.864) and significant positive correlations in SA/mass (r > 0.821) were found with the annual mean temperature from 18 months of age onwards and in the overall mean age. CONCLUSION: This study suggests that WHZ and SA/mass variation may be influenced by ecogeographical factors in this Chilean sample.