There is currently limited evidence showing the considerable length of time taken in some cases to reach a diagnosis of homocystinuria and the level of patient satisfaction regarding access to information, treatment options and medical care.  This survey is important to highlight the current situation and has been prepared in consultation with a Key Opinion Leader (KOL) in Europe together with input from HCU Network America, to ensure the information gathered can be used globally to help support improved care for all homocystinuria patients.