Background: Over the last years the way in which patients with chronic physical illness respond to their illness (illness behavior) has been explored by several studies. This study sought to examine characteristics of illness behavior and to investigate the association between illness behavior and psychosocial and clinical variables among asymptomatic HIV-infected subjects. Methods: Seventy-three asymptomatic HIV+ outpatients completed self-report questionnaires to evaluate illness behavior (Illness Behavior Questionnaire), psychological stress symptoms (Brief Symptom Inventory), personality variables (External Locus of Control and Courtauld Emotional Control Scales) and social support (Social Provision Scale). Results: Psychological morbidity (‘caseness’ = 34%) was associated with a pattern of illness behaviour characterized by conviction of disease progression, irritability, dysphoria, psychological perception of illness and low denial. Individual capacity to express emotions, adequate levels of social support and low levels of depression, as well as clinical variables (high number of CD4+ cells, recent notification of HIV infection and nonintravenous drug use category) influenced a more adaptive illness behaviour. Conclusions: Psychosocial variables resulted to influence the tendency to interpret illness in a nonadaptive way in asymptomatic HIV-infected subjects. Such variables merit to be routinely examined within the doctor-patient relationship in AIDS clinics.