Serum ferritin level at diagnosis was available in 185 patients with primary myelofibrosis (PMF); twenty-two (12%) patients had serum ferritin >1,000 ng/mL and 32 (17%) were red blood cell (RBC) transfusion-dependent. As expected, RBC transfusion need and increased serum ferritin displayed strong correlation (P < 0.0001); in addition, the latter but not the former correlated with advanced age (P < 0.0001). During median follow-up of 28 months (range 0.5-231), peak serum ferritin levels exceeded 1,000 ng/mL in 41 (22%) patients. On multivariable analysis that included age as a covariate, RBC transfusion need at diagnosis (P < 0.0001), but not increased serum ferritin or transfusion load, predicted shortened survival. The prognostic relevance of RBC transfusion need was independent of the International Prognostic Scoring System and was also illustrated for leukemia-free survival (P = 0.003). In PMF, the presence of a more severe erythropoietic defect, and not iron overload, has additional adverse prognostic value.