To predict leukemic transformation (LT) we evaluated easily detectable diagnostic parameters in 338 patients with primary myelofibrosis (PMF) followed in the Latium region (Italy) between 1981 and 2010. Forty patients (11.8%) progressed to leukemia, with a resulting 10-year leukemia-free survival (LFS) rates of 72%. Hb (≤ 10 gr/dL), and circulating blasts (≥ 1%) were the only two independent prognostic for LT at the multivariate analysis. Two hundred-fifty patients with both the two parameters available were grouped as follows: low risk (none or one factor) = 216 patients; high risk (both factors) = 31 patients. The median LFS times were 269 and 45 months for the low and high-risk groups, respectively (P < 0001). The LT predictive power of these two parameters was confirmed in an external series of 270 PMF patients from Tuscany, in whom the median LFS was not reached and 61 months for the low and high risk groups, respectively (P<.0001). These results establish anemia and circulating blasts, two easily and universally available parameters, as strong predictors of LT in PMF and may help to improve prognostic stratification of these patients particularly in countries with low resources where more sophisticated molecular testing is unavailable.