Climate change and obesity are two major concerns for policy makers globally, but can climate change be a driver of obesity? This is what our analysis tries to establish. To this purpose, we exploit inter-annual variations of the Body Mass Index (BMI) for children and adults in 134 countries over 39 years, to study to what extent changes in air temperature and precipitations affect obesity. Using panel data econometrics and exploiting both within- and cross-country variations in BMI, we uncovered a robust U-shaped associationbetween temperature and the BMI of girls, boys and women, but failed to detect any significant effect of precipitations. Our analysis also reveals that the impact of temperature on BMI, particularly for girls and women, is robust to the inclusion of other determinants of obesity stressed by the existing literature, such as GDP per capita, fertility, and agriculutral productivity, suggesting that mean air temperature is directly associated with, and may have an independent effect on, BMI.