In an attempt to ascertain whether the presenting features of idiopathic myelofibrosis (IM) have changed in recent years, 2 groups of patients diagnosed with IM in a single institution in different time periods were compared. The first group included 53 patients diagnosed from 1975 to 1986, and the second included 56 patients diagnosed from 1987 to 1997. No significant differences were observed between the two groups with regard to age, gender, delay from first symptoms to disease diagnosis, peripheral blood hematological values and serum biochemical parameters. Patients diagnosed prior to 1987 presented more often with constitutional symptoms (fever, night sweats, weight loss), but the difference did not reach statistical significance. These latter patients had, however, a higher frequency of splenomegaly (91% vs. 73%, p=0.01) and hepatomegaly (79% vs. 48%, p=0.002), and were more often in the osteosclerotic phase at diagnosis (p=0.05) than patients more recently diagnosed. Finally, no significant differences were found between both groups in either the distribution by prognostic scores or survival. The above results seem to indicate a trend towards a less florid clinical picture of IM at presentation in recent years. This, however, does not result in a longer patient survival.