The psychological and physical demands of coping with medication side effects and comorbid illnesses can be overwhelming and may influence behaviors, such as medication adherence, substance use, sexual risk behavior, and exercise that, in turn, affect health outcomes. Cross-sectional and prospective studies among diverse populations of persons living with HIV suggest that these behavioral mechanisms may be associated with HIV disease progression. The motivation to change behavior is often highest in the immediate aftermath of a stressor. However, over time the motivation to continue a particular behavior change is often challenged by habits, environmental influences, and psychosocial factors. Furthermore, a number of studies suggest that behavioral mechanisms may mediate the relationship between psychosocial variables (e.g., stress, depression, coping, and social support) and disease progression in HIV. Thus, developing clinical interventions that address these psychosocial factors and enhance protective health behaviors and reduce behaviors that convey risk to health are likely to lessen overall morbidity and mortality among patients living with HIV/AIDS.