Billing-code-based research, although imperfect, might be a valid measure of trends in disease prevalence and outcomes for an “orphan” disease. The term “orphan” signifies a condition with low prevalence in the population. This indicates both that few clinicians are interested in or capable of studying or treating the disease and that resources to make advances in the care of patients with orphan diseases are limited. There are other consequences of rarity that prevent progress in orphan conditions. For example, it is readily recognized that frequency-based statistics are more challenging to compute precisely for uncommon diseases. Perhaps less well appreciated is the confusion created by the language used to describe, report, and categorize a rare condition.