Context: Over the last several decades, we have observed an increase in the number of young patients with myeloproliferative neoplasms. The lack of information about clinic-hematological manifestations and outcomes requires a boost of common efforts between specialists. Objective: Determination of clinical hallmarks of primary myelofibrosis (PM) in patients under 40 years of age. Design: We performed this retrospective, clinico-analytical study and evaluated the data of 46 patients with PM, registered at the Department of Hematology of the Institute of Oncology in the Republic of Moldova. Setting: In Moldova, all patients with the diagnosis of hematological malignancies are followed up by the doctors from the Department of Hematology of the Institute of Oncology. These patients are managed at the Consultative Diagnostic Center outpatient and inpatient wards. Patients or Other Participants: At the moment, there are 450 patients with PM, including 46 young persons. These are the newest data that enroll all patients and newly diagnosed young patients with PM. We divided them into three groups according to age: 18–20, 21–30, and 31–40 years. Main Outcome Measures: The data analysis allowed us to formulate the hypothesis, which indicated a correlation between changes in the complete blood count (CBC) and splenomegaly, hepatomegaly, and long-term outcomes. Results: There were 11 male and 35 female patients. The major features of the first group were massive splenomegaly dominating in all 5 (10.9%) patients and mostly normal CBC values. In the third group, we observed elevated hemoglobin levels in 6 cases (13.0%) and frequent thrombocytosis in 24 (52.1%) cases. Massive splenomegaly was detected in 9 (19.6%) cases and normal spleen size in 3 (6.5%) cases. Two patients underwent splenectomy. Histological investigations revealed fibrosis MF 1–2 and hypercellular bone marrow in almost all cases. Thrombocytosis and splenomegaly of various sizes were found in the entire group of patients aged 21–30 years. Conclusions: This analysis did not reveal a correlation between the proliferative syndrome and the degree of leukocytosis and thrombocytosis. The disease may start with initial changes in the CBC, which should alert any specialist. All these patients remain under observation in our department.