In a cohort of 773 primary myelofibrosis (PMF), we determined the contribution of the rs1024611 SNP of CCL2—one of the most potent immunomodulatory chemokines—to the clinical and biological characteristics of the disease, demonstrating that male subjects carrying the homozygous genotype G/G had an increased risk of PMF and that, among PMF patients, the G/G genotype is an independent prognostic factor for reduced overall survival. Here, CCL2 is linked to primary myelofibrosis.