As antiretroviral treatment has led to decreased morbidity, HIV testing policy has increasingly shifted towards routine, provider-initiated approaches. Yet, few studies have examined the acceptability of provider-initiated HIV testing in the intensive, or critical care setting, where knowledge of HIV status is likely to impact on clinical management but explicit consent for testing is difficult to obtain. We conducted qualitative research in an urban hospital and clinic in Johannesburg. In-depth interviews were conducted among HIV testing clients (n = 20), recently discharged critical care patients (n = 13) and family members of critical care patients (n = 14). One focus group discussion was held with health care providers (n = 10). HIV testing in critical care was viewed as acceptable but challenging to implement. An overarching theme of ambivalence emerged from patients and families, who saw HIV testing as a pre-requisite to appropriate clinical care, but were concerned about the quality of its delivery. While providers were aware of the current "no testing without consent" policy, they expressed frustration in cases when testing was in the patient's best interest but consent could not be obtained. Furthermore, providers found it stressful to weigh up patient confidentiality against medical necessity when assessing patients' "best interests". Without specific guidelines, they often developed pragmatic, ad hoc ways to resolve dilemmas around testing in critical care. Our findings suggest that HIV testing guidelines specific to the critical care setting may help providers do their jobs more ethically and transparently. Provider-initiated approaches are likely to be acceptable to patients and may improve clinical outcomes, but training and support in policy implementation and ethical decision-making are essential.