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I read the article by Macaulay and colleagues titled ‘‘An Update on the Management of Pulmonary Arterial Hypertension and the Pharmacist’s Role’’ with great interest, especially their discussion of the role of the pharmacist in ensuring safe and effective medication delivery to this unique patient population. However, I believe there were several errors in their introduction and discussion of the epidemiology of pulmonary arterial hypertension (PAH). The authors stated that the estimated prevalence of the disease, worldwide, was ‘‘15 to 52 million’’ patients. The actual estimate of prevalence of WHO group 1 PAH in adults has been reported between 15 and 52 cases per million individuals. Additionally, a more recent review of the US Registry to Evaluate Early and Long-term Pulmonary Arterial Hypertension Disease Management (REVEAL) suggested a conservative estimate of 12.4 cases per million. Similarly, the authors stated that there are approximately 200 000 new diagnoses of PAH annually in the United States, but the incidence reported by Frost et al was only 2.3 cases per million for WHO group 1 adult patients in the United States. This suggests the actual number of new diagnoses is much lower, likely less than 1000 new cases per year based on the current US population estimates. Finally, the citation that accompanies these statements is an article by Ling et al, which analyzed results from a patient registry in the United Kingdom and Ireland. Their estimated prevalence was 6.6 cases per million in 2009, and they did not report on the incidence of new cases of PAH in the United States. Although these errors do not detract from the overall value of the author’s contribution, correcting them may further emphasize the rarity of PAH and further support the notion that pharmacists, as drug experts, may have a significant impact on patient safety and outcomes when involved in the initial and ongoing management of this condition.