Key points: Over the course of the five winter seasons from 2012–13 to 2016–17, 91,255 hospital stays with a diagnosis of influenza were identified by the PMSI in mainland France. The average incidence per season, across all age groups, was 28.5 hospitalizations per 100,000 inhabitants; the main results show, on the one hand, significant variations in hospitalization incidence by age across epidemic seasons, and, on the other hand, differences among age groups in terms of severity and impact (proportion of patients transferred to intensive care, case fatality rate, average length of stay); variations across epidemic seasons were consistent with known differences in susceptibility to circulating influenza subtypes, with a major impact of subtype A(H3N2) in the elderly and B viruses in children; Patient age affects severity, with a steady increase in case fatality rate from 0.5% to 10%, as well as the frequency of intensive care admissions, which is higher in the intermediate age groups of 40 to 79 years (19%) than in other age groups, particularly those aged 80 and older (6%); age is also a significant factor in longer hospital stays, ranging from 3.4 days for those under 20 to 11.5 days for those aged 80 and older; significant regional disparities were observed, notably with the highest incidence of hospitalizations in southeastern France and a higher proportion of intensive care admissions in the Île-de-France and Centre-Val de Loire regions; analysis of hospitalizations with a diagnosis of influenza through the PMSI provides important insights for interpreting influenza surveillance data, which are not available through other surveillance systems. A systematic annual analysis of hospitalized patients using the PMSI would provide, at the end of the season, an age-stratified indicator of the epidemic’s impact on the hospital system.