Introduction - In France, the epidemiological characteristics of acute intussusception (AI) are not well understood. Method - The primary objective was to estimate the annual incidence of AI in children under 1 year of age. This was a prospective observational epidemiological study with comprehensive registration of suspected cases of AAI in children under 1 year of age over a four-year period, from April 1, 2008, to March 31, 2012, in the Grand-Est region (98,600 births/year). All suspected cases of ARI were classified according to the Brighton Classification (5 levels of certainty) by a diagnostic committee of independent experts. Results - From April 1, 2008, to March 31, 2010, 109 suspected cases of ARI were included; 80 cases (73.4%) were classified as level 1 (certain cases). The sex ratio (boys/girls) of the cases was 1.7, and the peak incidence of AII occurred between the ages of 6 and 8 months (29.9%). The annual incidence rate of confirmed IIA (Level 1), with and without established anatomical causes, per 1,000 live births was 0.48 for the first year of the study and 0.34 for the second year of the study. The annual incidence rate of confirmed idiopathic IIA (level 1) was 0.43 for the first year of the study and 0.31 for the second year of the study. Conclusion - Our results are consistent with data in the literature. Our study, which is scheduled to continue until March 31, 2012, will ultimately allow us to analyze trends in incidence and identify risk factors for AII in children under 1 year of age. (RA)