['Comorbidities have been shown to play an important role in the prognostic assessment of several hematologic conditions; however, the role of comorbidities in primary myelofibrosis has not been studied. The objective of the current study was to evaluate the prevalence and impact of comorbidities in patients with primary myelofibrosis (PMF) using the Adult Comorbidity Evaluation-27 (ACE-27).', 'In this retrospective observational cohort study, a total of 349 consecutive patients with a confirmed diagnosis of PMF who presented to the study institution from 2000 to 2008 were evaluated. The authors evaluated the frequency and severity of comorbidities in these patients and assessed their impact on survival in a bivariable model that included the ACE-27 and Dynamic International Prognostic Scoring System scores as covariates.', 'Approximately 64% of patients had at least 1 comorbid condition, and diseases of the cardiovascular system (63%) were most common. Comorbidities had a significant negative impact on survival (P <\u2009.001). Patients with severe comorbidities had twice the risk of death as those with no comorbidities. When stratified by demographic and clinical characteristics, comorbidities were found to be significantly associated with worse survival in patients aged\u2009< 65 years (P <\u2009.001) and those with an ECOG performance status\u2009<\u20091 (P\u2009<\u2009.001). In a multivariable model that included the ACE-27 and Dynamic International Prognostic Scoring System scores, comorbidities retained a significant association with shorter survival (P ≤\u2009.001).'] Do comorbidities predict worse prognosis in patients with primary myelofibrosis?