In summary, interpretation of these two studies and their apparently conflicting findings is limited as a consequence of a number of factors, including case definition, case ascertainment, methods used to assess socioeconomic status, sample size and lack of a control group. They neither confirm nor refute the hypothesis that the risk of Perthes' disease is increased among children living in deprived circumstances. What is the take-home message for the orthopaedic surgeon managing children with Perthes' disease? Despite a large number of published studies, the causes of Perthes' disease remain elusive. Unfortunately, the limitations identified in these two studies are replicated in the literature, with relatively few adequately powered prospective case control studies, and none to our knowledge that have involved more than one centre. Although confounding may explain the associations observed with maternal smoking, this does emerge as a consistent finding in the larger case control studies, thus adding to the already substantial body of evidence linking parental smoking to adverse health consequences for children.