Surgical mesh materials made from fibres of polypropylene (PP) have been widely used for over fifty years. However in recent times the use of these materials has been called into question for certain surgical operations, known as "pelvic organ" or "transvaginal" procedures. This article reviews the current state of knowledge and uses some simple biomechanics analysis in order to make recommendations for future work. My conclusion is that the failure rate of PP mesh in pelvic organ products is unacceptably high whilst being much lower when it is used for hernia repair. The precise mechanical environment is difficult to quantify but a tentative conclusion is that failure by purely mechanical mechanisms (fatigue and creep) is unlikely. There is some evidence for environmental degradation (i.e. stress-corrosion) but this is highly contested in the literature. On balance my conclusion is that stress-corrosion failure is the most likely explanation but currently no experimental results exist to prove conclusively that this failure mechanism occurs in vivo. Further work is needed, especially the analysis of explanted material, to resolve this urgent problem.