The Humanitarian Use Device or HUD program was established in 1990 with passage of the Safe Medical Devices Act and creates an alternative pathway for getting market approval for medical devices that may help people with rare diseases or conditions. As defined by 21 CFR 814.3(n), a HUD is a “medical device intended to benefit patients in the treatment or diagnosis of a disease or condition that affects or is manifested in fewer than 4,000 individuals in the United States per year.” In order to obtain HUD designation, the applicant must provide documentation, with appended authoritative references, to demonstrate that the device meets the definition of 21 CFR 814.3(n). In addition to the documentation describing the disease or condition, the applicant must also provide the proposed indications for use of the device, and the reasons why such a device is needed for the patient population. One aspect that has become increasingly difficult is if the HUD is proposed for an indication that represents a subset of a common disease or condition. In these situations, the applicant must demonstrate that the subset is an "orphan subset. " An "orphan subset" is a regulatory phrase used to describe the subset of individuals with a non-rare disease or condition on whom use of a device is appropriate, where use of the device on the remaining individuals with that disease or condition would be inappropriate given some intrinsic feature of the device (e.g., adverse event profile or mode of action). An "orphan subset" is not a readily identifiable subset or a group of patients who meet or do not meet the inclusion and exclusion criteria for a clinical study. Likewise, they are not patients with an unmet medical need. If the HUD application is designated, the applicant can then submit the HDE marketing application to the Center for Devices and Radiological Health (CDRH) or Center for Biologics Evaluation and Research (CBER) for marketing review.