OBJECTIVE To examine whether hiatal expansion and levator avulsion have a role in the causation of pelvic organ prolapse (POP). METHODS Data from studies which showed a strong association of hiatal expansion and levator avulsion were analysed for causation against an alternative view, POPcausation by ligament/connective tissue damage. RESULTS Some studies potentially fitted the "Regularity Theory of Causality"; i.e., an apparent cause, occurred with such regularity as to be considered a cause. However, these studies failed the logical requirement of "unconditional": all levator avulsions were to be followed directly by occurrence of POP, if the association were to be considered valid. Two studies which placed a large mesh behind the rectum and around puborectalis muscle greatly diminished levator expansion, but POP recurred in 78% of the women by 12 months. These results invalidated hypotheses of cause (levator expansion) and effect (prolapse). CONCLUSIONS Levator avulsion/hiatal expansion co-occurs with POP. The cause for both is likely inability of the birth canal to plasticize" sufficiently to prevent simultaneous damage to the hiatal muscles and surrounding fascias and ligaments, which explains the co-occurrence. Greater than 90% cure of POP by site-specific repair of up to 4 pelvic ligaments supported the alternative hypothesis of simultaneous damage to pelvic ligaments to cause prolapse.