Several observations have shown that patients with polycythemia have iron deficiency. Our objectives were to report the prevalence of iron deficiency and to evaluate the diagnostic performance of serum ferritin in polycythemia vera. This is a retrospective descriptive and analytical study carried out in the internal medicine department of the Henri Mondor Hospital, Aurillac, France. The study involved 114 patients with polycythemia, followed in the department from January 1, 2010 to December 31, 2021. To evaluate the diagnostic performance, the JAK2 mutation was considered as the gold standard of diagnosis. Thirty-three patients had polycythemia vera and 76 patients had secondary polycythemia. The mean age of the patients was 61.79 years (±15.44) with a sex ratio of 4.43. The overall prevalence of iron deficiency was 21.05%. The prevalence was 53% in polycythemia vera group and 1.32% in secondary polycythemia group. The risk of iron deficiency was high in polycythemia vera (OR =  115 ; 95% CI 14.4-918.2, p < 0.0001) and the sensitivity and specificity of serum ferritin were 52.63% and 100% respectively. Assessment of iron deficiency should be part of the initial evaluation of polycythemia. Iron deficiency had a high specificity during polycythemia vera.