Background: High altitude polycythemia is one of the altitude illnesses. Sana'a region is located at high altitudewhich reaches 3600 meters above the sea level. Objectives: To determine the hematological and clinical features of polycythemic patients residingin Sana'a region and to clarify the effect of high altitude in causing polycythemia. Methods: Hematological, clinical and demographic data were obtained from 30 polycythemic patients (26 males, 4 females, aged 26 to 85 years residing Sana'a regionand referred to the National Centre of Public Health Laboratories in Sana'a city for the firsttime venesection. Results:All studied samples showed high hemoglobinlevels (mean 18.85 g/dL for both sexes), normal platelet counts (228 and 267 x10 9/L for males and females, respectively),normal white cell counts in 96.7% of the cases (means 6.01 to 5.98 x10 9/L). Their clinical features showed predominance of headache, ruddy cyanosis, dyspnea and night sweating by 86.7%, 76.7%, 70% and 60%, respectively. Hypertension, joint pain, renal disease, peptic ulcer were less commonly mentioned by 36.7%, 20%, 13.3%, and10%, respectively. Hemorrhage, pruritus, splenomegaly, heart disease andliver disease wereobserved by only 6.67% each. Conclusions: Findings suggest thatsecondary polycythemia is predominant among polycythemicpatients due to the high altitude of Sana'a region. Findings needs to be confirmed bystudyinga larger sample and extended to investigate the erythropoietin level and JAK2V617F mutation for accurate diagnosis.