Pilot testing for the registry indicated that a 2-pronged approach could be used to identify all newly diagnosed and existing ALS cases in the United States. The first approach, launched in 2009, uses large, existing national administrative databases (ie, Medicare, Medicaid, Veteran Benefits Administration, and the Veterans Health Administration) to identify patients with ALS. Because there is no blood test for ALS and the diagnosis is largely based on signs, symptoms, and neurophysiologic tests (eg, electromyograms), this approach uses a pilot-tested algorithm that, when applied to the databases, separates patients into 3 categories: definite ALS cases, possible ALS cases, and non-ALS cases. Patients with definite cases are automatically entered into the National ALS Registry. Patients for whom there is not enough information to determine whether they have ALS are considered possible cases and are reevaluated when subsequent years of administrative data become available. If these patients are later determined to be definite cases, then they are entered into the registry. Patients who are determined not to be definite cases are not included in the registry.