Public health surveillance is an essential tool for assessing, controlling, and preventing disease. In the United States, public health surveillance has evolved from a focus on monitoring infectious diseases to also tracking injuries, chronic diseases, birth defects, environmental and occupational exposures, and risk factors. 1 Despite this evolution of surveillance topics, many conditions still are not notifiable to federal public health officials nor are there surveillance systems in place to capture such conditions. The lack of morbidity data for nonnotifiable conditions makes it difficult to access accurately the populations at greatest risk and the true economic and societal burden of such diseases. New approaches are needed to more accurately quantify nonnotifiable conditions of interest in the United States, such as amyotrophic lateral sclerosis (ALS). ALS, also known as Lou Gehrig disease, is a rare disease that affects the upper and lower motor neurons and usually leads to death within 2 to 5 years after diagnosis. 2 In 2008, the US Congress passed the ALS Registry Act, 3 intended to create a national ALS registry to better describe the incidence and prevalence of ALS, define demographic characteristics of those with ALS, and examine risk factors that may be related to the development of ALS, such as environmental and occupational exposures. Even though the act did not make ALS a notifiable disease, it did allow for the creation of a national population-based registry to collect and analyze data regarding persons living with ALS in the United States. In 2009, the federal Agency for Toxic Substances and Disease Registry (ATSDR), a sister agency of the Centers for Disease Control and Prevention (CDC), launched the National ALS Registry. This registry undertook a novel approach to quantify the burden of ALS using data from national administrative sources and a self-enrollment web portal. Data from both sources are merged and de-duplicated to ensure an accurate case count.