Background: Allogeneic hematopoietic stem cell transplantation (HSCT) offers potentially curative therapy for numerous malignant and non-malignant diseases. The number of survivors and length of follow-up after successful HSCT is continually increasing. Hematopoietic stem cell transplantation can induce damage of various organs and tissues – from minimal potentially progressive subclinical changes to life-threatening conditions. The aim of this thesis was the evaluation of the prevalence of metabolic syndrome (MS) among survivors of allogeneic HSCT. Patients and methods: We analyzed 74 patients with a median age at transplant of 35 years, who had been followed for a median of 5 years (2–23 years) after allogeneic HSCT. MS was defined according to the National Cholesterol Education Program’s Adult Treatment Panel III (NCEP ATP III) criteria and by the International Diabetes Federation (IDF) definition. Results: The prevalence of MS among HSCT recipients was 40.5% applying the NCEP ATP III definition and 39.2% the IDF, a 2.02-fold increase compared to the general Slovak population. MS was more common in men. The most common MS features were abdominal obesity, hypertriglyceridemia and hypertension. The lowest prevalence of MS was in the age group of 20–29 years; and the highest prevalence in the age group of 60–69 years. The 10-year cumulative incidence of MS was 32.5%. The most significant risk factor for MS was total body irradiation, positive family history and age > 40 years at HSCT. Seven patients (9.45%) developed cardiovascular complications. The median 10-year general cardiovascular risk scores for males and females were found to be 13.3% and 6.68%, respectively. Conclusions: Detected increased prevalence of metabolic syndrome after allogeneic HSCT in patients surviving more than 2 years after this procedure may provide next stimulus to promote longer follow-up studies and to design of interventions to prevent late effects among survivors of serious hematologic diseases.