Introduction: HIV counseling and testing is a gateway to prevention, treatment, care and support services and an essential tool in the control of HIV/AIDS epidemic. Currently HIV status has been very low which cannot be achieved only through the traditional VCT alone and another alternative, routine HIV testing and counseling of patients, also called provider initiated HIV Counseling and testing is proposed. Objective: To assess the acceptability and associated factors of provider initiated HIV counseling and testing among OPD clients with possible clinical sign of HIV infection in West Arsi zone, Ethiopia. Methods: Facility based cross sectional study was conducted on outpatient department clients with possible clinical sign of HIV infection in 6 selected health facilities in West Arsi Zone, Ethiopia. The health facilities were selected randomly; study subjects who came to the health facilities were consecutively interviewed. Data collected by a pre-tested, structured interview questionnaire. Regression model was used to assess factors associated with acceptability of provider initiated HIV Counseling and testing. Results: A total of 539 clients were interviewed with a response rate of 92.3%. The majorities (66.4%) were married, major age distribution was range from 25-29 (29.1%) and the main religion was Muslim (66.2%). Knowledge on importance of provider initiated HIV Counseling and testing was low. The willingness and overall acceptability rate was 86.5%, and 83.1% respectively. The major perceived barriers for acceptability were mainly thinking self as not being at risk, followed by fear of stigma and discrimination. On adjusted covariates of acceptability, acceptability of PIHCT was found to be associated with having information on PIHCT service (OR=0.36; CI=0.22-0.60), less and much support for PIHCT (OR=0.30; CI=0.11-0.85 and OR=0.31; CI=0.12-0.77) and tested for HIV before (OR=0.20; CI=0.10-0.41) Conclusion and Recommendations: The acceptability noticed in this study is high. The major perceived barriers for acceptability was thinking self as not being at risk. Having information on PIHCT service, tested for HIV before, and extent of support for PIHCT were found to be important predictors of acceptability of PIHCT. Hence, intensive IEC/BCC and promotional activities through different means should be in place to raise level of awareness, support and routine testing to facilitate its acceptability and reduce major barriers that affect PIHCT service utilization at all level.