The complexity of endo-perio lesions reflects the relevance of a close developmental relationship between the pulp and periodontal tissues. A review of the literature was undertaken to discuss the complex and dynamic nature of normal anatomical and pathological pulp and periodontal intercommunication pathways. This interrelationship was then correlated with the criteria followed in previous classifications for endo-perio lesions. Based on this analysis, the most reliable criteria and the missing patterns of endo-perio lesions were identified, and then described in a proposed new classification. Keywords: classification, endo-perio lesions, periodontal, pulp