Cambodia has one of the highest prevalence rates of HIV in Asia and is scaling up HIV testing. We conducted a cross-sectional survey with 358 health care providers in Phnom Penh, Cambodia to assess readiness for voluntary testing and counselling for HIV. We measured HIV knowledge and attitudes, and predictors of intentions to take a sexual history using the Theory of Planned Behaviour. Over 90% of health care providers correctly answered knowledge questions about HIV transmission, but their attitudes were often not positive towards people living with HIV. The Theory of Planned Behaviour constructs explained 56% of the variance in intention to take a sexual history: the control providers perceive they have over taking a sexual history was the strongest contributor (51%), while social pressure explained a further 3%. Attitudes about taking a sexual history did not contribute to intention. Interventions with Cambodian health care providers should focus on improving skills in sexual history-taking.