BackgroundA timely diagnosis is a critical step to ensure a proper access to expert clinical management for patients. However, diagnosing rare diseases (RD) is a major challenge, as these diseases are extremely diverse in their expression, cause, semiology and nosology. Today, the development of digital technologies offers genuine opportunities for improving diagnosis and care in a sector with urgent needs. However, developing and testing digital solutions would only be possible for a limited number of Rare Diseases (RD). ResultsThe approach presented in this article aims at proposing an ethical and rational way of defining a subset of “priority” rare diseases to focus on, based on pathologies for which an established and effective standard of care management is defined. Two types of management were considered: the existence of a medicinal product specifically targeting the disease; and / or the existence of authoritative clinical guidelines in France. Our work led to the establishment of a list of 251 RD for which a delayed diagnosis would be especially detrimental. ConclusionIt remains now to establish whether the diagnosis of these RD is especially delayed, or not, before setting up targeted initiatives to reverse the situation. Clarifying choices when taking initiatives to develop solution in a field with so many unmet needs is an element of an ethical approach.