Follow-up in a 46-year-old patient clinically presenting as ET with a platelet count of 951 × 10⁹/L, a hemoglobin/hematocrit value at the upper limit, a positive JAK₂ mutation status, and an erythropoietin level of 2.0 U/L. There was an increase of the hematocrit and white blood cells (WBC) starting after more than 2 years of observation with manifestation of overt PV requiring treatment with interferon (IFN).