Aims: There are about 350 million people with HBV infection in the world.. 5% or about 15-20 million people of them are co-infected HDV. Every year an average of 7500 people are detected HDV new infection and 1,000 people die due to HDV infection in the United States. The Middle East, Pakistan, Central and Northern Asia, some areas of Africa, have high prevalence of HDV infection. North America, Northern Europe, Southern Africa and East Asia have low prevalence of HDV infection. There is 70-90%higher risk of liver cirrhosis in patients with HBV/HDV co-infection than patients with HBV infection. Comparative study of cirrhosis stage in patients with HBV infection and HBV/HDV co-infection Methods: Our study continued from January 2015 to March 2017 and we measured liver fibrosis stage in patients with HBV infection and HBV/HDV co-infection using a Fibroscan (Fibroscan 502 Touch, Echosens, Paris, France) who are controlled in Happy Veritas Clinic and Diagnostic Center. When we measured liver fibrosis stage in 5504 patients with HBV infection, 20% or 1115 of the patients is determined HDV co-infection . In our study in random sampling cases are selected 354 patients with HBV monoinfection and 177 of all patients have HBV/HDV co-infection. We selected parameters from patients medical histories in our study, such as serologic markers of HBV quantification of HBV and HDV in serum samples, blood test, liver function tests, and liver fibrosis stage. Summary statistics were perfomed using sPSS 22.0 siftware. Results: 354 patients 47.7 %(169) was men. Range with an average age of 44±17 (range 18-75 years old) were included the study. According to the comparative study in laboratory tests, ALT level was HBV - 44 (36; 51.5) and HBV/HDV co-infection 61 (39.8; 97.5), AST level was HBV - 39.1(30; 83) and HBV/ HDV co-infection - 50 (33.1; 77.8), Platelet count was HBV- 193±66 and HBV/HDV - 181±62.8. When we compared liver fibrosis stage were HBV- F0 67(37.9%), HBV/HDV-F0 57(32.2%), HBV-F1 22(12.4%), HBV/HDV-F1 17(9.6%), HBV-F2 39(22%), HBV/HDV- F2 39(22%), HBV-F3 29(16.4%), HBV/HDV-F3 41(23.2%), HBV- F4 20(11.3%) and HBV/HDV -F4 23(13%). In table 1 shows the difference of liver fibrosis by age group. Conclusions: 65.5% of all patients with HBV/HDV co-infection are from 30 to 50 years old. Liver fibrosis of patients with HBV/ HDV co-infection is a higher 11.88kPa than patients with HBV mono-infection. Our study shows that, the hepatitis is more severe in patients with HBV/HDV co-infection and the platelet count is less than HBV infection only.