Uncertainty is a chronic and pervasive source of psychological distress for persons living with HIV. Numerous sources of heightened uncertainty, including complex changing treatments, ambiguous symptom patterns, and fears of ostracizing social response, play a critical role in the experience of HIV-positive persons and are linked with negative perceptions of quality of life and poor psychological adjustment. Currently, research on uncertainty in HIV fails to explicate the uncertainty experience over time. Because the uncertainty of HIV varies over the course of the illness, an explicit consideration of the sources of uncertainty over the HIV illness trajectory is needed to forecast the informational and stress management needs of persons facing uncertainty about HIV illness. A biopsychosocial model developed to characterize the HIV stigma trajectory provides a useful framework modified to depict uncertainty across the HIV illness experience. Uncertainty in four phases of the HIV illness trajectory are differentiated: (a) at risk, (b) diagnosis, (c) latent, and (d) manifest.