To guide public policy, rare diseases, a rising global public health concern, require an evidence-based estimate of global point prevalence. Forecasting disease outbreaks is extremely useful for efficiently planning and supplying resources. Rare diseases (RDs) are diverse, heterogeneous, and spread over the globe. Few are preventive or curable, the majority are chronic, and many lead to premature death. Despite their diversity, RDs have some characteristics in common due to their rarity, which needs a comprehensive public health strategy. The diversity of the data, which is derived from a variety of disparate information sources that are not standardized or difficult to combine, such as published case reports or systematic reviews, patient registries, expert opinions, and other anecdotal evidence, makes estimating the global point prevalence of RDs difficult. As RDs become a global policy objective of leaving no one behind, refinement of the epidemiological estimate of RDs is timely.