Background: Exposure to hepatitis B virus (HBV) or human immunodeficiency virus (HIV) infection is common among hepatitis C virus (HCV)-infected Intra venous drug users (IVDUs); however there exist only a few data about frequency and risk factors of HCV, occult HBV infection (OBI) and HIV among IVDUs. Objectives: This study aimed to investigate the prevalence and associated risk factors for OBI and HIV infections among Iranian HCV infected IVDUs. Methods: Serum samples were screened for the presence of hepatitis C virus antibody (HCVAb), hepatitis B core antibody (HBcAb), hepatitis B surface antigen (HBsAg), and human immunodeficiency virus antibody/antigen (HIVAb/Ag) using enzyme linked immunosorbent assay (ELISA). For detection of OBI, presence of HBV DNA among HBcAb positive/HBsAg negative subjects was determined using nested polymerase chain reaction (PCR). Results: Among all subjects, 94 cases (53.5%) were positive for HCVAb from which 7% and 23.4% were positive for HCV/OBI and HCV/HIV co-infections, respectively. A significant association existed between HCVAb with type of drug, sharing syringes and needles and a history of imprisonment. In the case of HCV/OBI co-infections, the only significant correlation was between sharing a syringe and occult hepatitis B infection. Also no significant association existed between risk factors and HCV/HIV co-infections. Conclusions: the present data documented an alarming prevalence of HCV and HIV as well as co-infections among IVDUs, which emphasizes the requirement for expansion of public health interventions for this at-risk population. Despite previously high prevalence reported for HCV/HBV/HIV triple infections among IVDUs, low prevalence of triple HCV/OBI/HIV infections was obtained. The reason for this difference may be related to the effect of HCV on HBV expression in case of OBI which had been suggested previously.