The Sampson Theory for the pathogenesis of endometriosis is the oldest, but remains the most widely popular and accepted hypothesis. It is based on observations made as early as in 1938, that that endometriotic implants in the pelvis arise from retrograde (reversed) menstruation of endometrial tissue through the fallopian tubes. The finding that women with endometriosis have larger volumes of retrograde material than healthy women might be another stone in the mosaic. Similarly, studies showing that women with cervical or vaginal outlet obstructions have a higher risk of endometriosis support this thesis. The Sampson Theory is certainly not the only explanation as it does not explain all locations of endometriosis deposits (in surgical scars, and in distant organs ) which suggest contribution by other factors, including the possibility of direct transmission and implantation of endometrium into surgical sites, blood and lymphatic borne transmission, genetic and immunologic factors and the conversion (metaplasia) of cells on the surface of the peritoneum (the membrane that envelops pelvic structures) to endometrium …to mention but a few. Notwithstanding the above, the Sampson Theory is probably operative in the vast majority of cases of endometriosis and is no no means an “outmoded” concept.