Background: The incidence of acute myocardial infarction (AMI) varies according to seasonality, being higher in winter. The effect of sex on this phenomenon is not clear. Aim: To evaluate the effect of seasonality in men and women hospitalized for AMI at different ages. Material and methods: We included all patients with a primary diagnosis of AMI admitted in public and private hospitals in Chile during 2002-2011 (codes I21-I22, of the tenth international classification of diseases). We obtained data from the National Discharge databases available at the Ministry of Health website. We estimated the number of discharges per month and per seasonality (cold /template), and the Standardized Incidence Ratio (SIR) with the formula: number of observed cases/expected cases (average annual hospitalizations), stratified by sex and age (Background: The incidence of acute myocardial infarction (AMI) varies according to seasonality, being higher in winter. The effect of sex on this phenomenon is not clear. Aim: To evaluate the effect of seasonality in men and women hospitalized for AMI at different ages. Material and methods: We included all patients with a primary diagnosis of AMI admitted in public and private hospitals in Chile during 2002-2011 (codes I21-I22, of the tenth international classification of diseases). We obtained data from the National Discharge databases available at the Ministry of Health website. We estimated the number of discharges per month and per seasonality (cold /template), and the Standardized Incidence Ratio (SIR) with the formula: number of observed cases/expected cases (average annual hospitalizations), stratified by sex and age (