Background: Indoleamine 2,3-dioxygenase (IDO) catalyzes the rate-limiting step in the metabolism of tryptophan along the kynurenine pathway. IDO is a key factor maintaining immune tolerance and expression correlates with poor clinical outcome in different types of cancer and hematological malignancies. Nowadays, not enough attempts have been made to evaluate IDO expression and its prognostic score value. We assessed the impact of the IDO expression on clinical outcome in patients with Hodgkin lymphoma (HL). Methods: The case group included 23 patients (5 male and 18 female) with HL (median age: 19-60 years, range: 39.5). With early stage were diagnosed 52.2% and 47.8% with advanced. Only 26% cases had B-symptoms. ABVD or BEACOPP (14/esc) were administered as a first-line therapy. In 65.2% and 34.8% cases, achievement remission and progression disease after treatment, respectively. The relative mRNA expression levels of IDO were measured in pre-treatment tumor tissue specimens from HL patients using real-time qPCR analysis. Results: The mRNA expression of IDO was found in 15 cases (65.2%) and further this group was considered as IDO-positive. The presence of IDO expression was significantly associated with advanced stage of disease and B-symptoms (p<0.05). The relapse was more frequently found in cases with IDO+ compared IDO- HL (30.47% versus 4.3%, p< 0.05). 13% patients with IDO+ expression died and had an early relapse or refractory disease. ROC analysis revealed that IDO+ expression in the tumor is an important marker which is associated with reduced progression-free (PFS) and overall survival (OS) in HL patients (Se=87.5 %; Sp=78 %; AUC=0.85). 5-year PFS for patients with IDO+ expression was 44% versus 89% of IDO- expression (p=0.0003). Two-sample comparison between the IDO+ versus IDO- expression was done by the Cox F-test. The difference was significant for PFS and OS (p=0.03). Conclusions: The obtained results suggest that the IDO-positive expression can predict clinical outcome in patients with HL and seems to be promising for the future studies.