HIV testing is an entry point to comprehensive HIV/AIDS prevention and care. In Uganda, Routine Testing and Counseling for HIV (RTC) is not widely offered as part of standard medical care in acute care settings. This study determined the acceptance of RTC in a medical emergency setting at Mulago national referral hospital. We interviewed 233 adult patients who were offered HIV testing. Overall, 83% were unaware of their HIV serostatus and 88% of these had been to a health unit in the previous six months. Of the 208 eligible for HIV testing, 95% accepted to test. Half the patients were HIV infected and 77% of these were diagnosed during the study. HIV testing was highly acceptable and detected a significant number of undiagnosed HIV infections. We recommend adoption of RTC as standard of care in the medical emergency unit in order to scale HIV diagnosis and linkage to HIV/AIDS care.