Familial erythrocytosis is a rare inherited disease characterized by an increased number of red blood cells, often also elevated hematocrite and hemoglobin. Patients have symptoms such as headaches, nausea, thrombosis and bleeding, which can lead to death. Von Hippel-Lindau tumor suppressor protein (VHL) is part of a complex involved in the degradation of proteins, including the Endothelial PAS domain-containing protein 1 transcription factor, which is activated in the presence of oxygen deficiency. Sequence variants in VHL gene can lead to the development of familial erythrocytosis type 2. In collaboration with the Specialized haematological laboratory of the Clinical department of hematology, internal clinic University Medical Centre Ljubljana, we established a diagnostic method for the VHL variants in patients with familial erythrocytosis. We optimized PCR, amplified fragments of VHL gene and sequenced then with Sanger method. The new diagnostic test was used to analyse four patients with unknown causes of erythrocytosis. Based on sequential reactions, we confirmed that none of the examined patients had a variation in the VHL gene and therefore we excluded familial erythrocytosis type 2. In the future, this molecular-genetic test, with other tests on different genes, could be used for routine screening of variants in patients with idiopathic erythrocytosis.