Background: Influenza is a contagious disease that runs a deteriorating and lethal course among high-risk groups such as HIV/AIDS patients. Influenza vaccination is significant among the high-risk groups, but there is inadequate information about vaccination among HIV/AIDS- patients. Objective: The aim of the study was investigating the effects of influenza vaccination on HIV/AIDS-stricken patients residing in Kermanshah Province, Western Iran. Materials and Methods: The present work was classified as a clinical trial. To perform the study, 134 HIV/AIDS-stricken patients were selected at the Counseling Center for Behavioral Disorders based in Kermanshah in 2014. The inclusion criteria were patients under antiretroviral treatment for at least 12 months' duration and availability of the participants in the study. 0.5 millimeters of influenza vaccine were injected into the deltoid muscles of the participants. One month before and after the injection, their blood samples were taken and stored at a temperature of –20 °C. The antibody titer tests were performed at the National Influenza Centre (NIC) based in Tehran, Iran, through the cold chain. After data collection, the SPSS Statistics 21 Software was utilized for data analysis. Results: In total 63.4% of the subjects were men and the rest (36.6) were women. The average age of the patients was 37.5 ± 8.5 years (men = 39.9±7.7 and women = 34±1.2). The results showed that the serum level of the anti-A (H1N1) antibody increased from 71.6% to 91.8% and that of the anti-B antibody went up from 70.1% to 92.5%. In addition, the results of t-test demonstrated that there was a significant difference between the levels of anti-B antibody titer and anti-A (H1N1) antibody titer before and after the influenza vaccination (P ≤ 0.05). Also, the means of CD4 and CI95% were significantly different before and after the injection (P ≤ 0.05). In this research, the CD4 count over 500 cells/mm3 rose from 22.2% to 32.8% before and after the vaccination, indicating a significant increase according to the t-test (P ≤ 0.05). Conclusion: From the presented, it can be concluded the CD4 count over 500 cells/mm3 increased after vaccination among HIV/AIDS-stricken patients. Therefore, the annual vaccination of HIV/AIDS-stricken patients against influenza can lessen the severity of pathogenicity, length of hospital stays, and mortality through stimulating the immune system and increasing the anti-Band anti-A (H1N1) antibody titers and CD4 cell counts.