I think most of the challenges are covered in the discussions of two friends above. I just want to add some specific consequences of not using the ICD standard. For one, it would make it more difficult to compare the performance of different healthcare organizations. For example, it would be difficult to compare the rates of a particular disease mortality between hospitals if they were using different coding systems. Secondly, it would be difficult to identify patients who are at high risk for a health condition such as heart attack if they are not being coded consistently for risk factors such as high blood pressure and cholesterol. And lastly, from the public health perspective, it would be difficult to target interventions to communities that are at high risk for certain diseases if the data on disease prevalence is incomplete or unreliable.