Endometriosis is a frequent pathology for which the dominant signs and symptoms are pelvic pain and infertility. The physiopathology remains the subject of controversy. Four physiopathological hypotheses have been put forward: regurgitation, metaplasia, induction and (vascular and lymphatic) embolization. The anatomical distribution of endometriotic lesions would appear to be fundamental for a better understanding of Sampson's menstrual regurgitation theory of endometriosis. Analysis of the results in the literature and comparison with our experience clearly shows that the distribution of endometriotic lesions is asymmetrical in several respects. Abdominopelvic anatomy and peritoneal fluid flow can explain this asymmetrical distribution of endometriotic lesions in the great majority of cases. These observations are a very strong argument in favour of the crucial role played by tubal regurgitation and the peritoneal fluid in the physiopathology of endometriosis. The similarity in anatomical distribution of endometriomas, superficial and deeply invasive endometriotic lesions would tend to indicate a common origin for these different types of lesions.