Hepatitis C and HIV/AIDS are among the most significant infectious diseases of our time. Psychiatric patients are often part of the higher risk population to contract these diseases, and patients who have contracted these diseases experience a wide variety of psychiatric problems associated with the underlying infection and with its treatment. The authors provide an overview of these infectious diseases and then describe the varying roles psychiatrists have in caring for these patients in the various settings of their work. The complexity of these patients presents a unique challenge to, and opportunity for, psychiatrists to integrate and coordinate their interventions with those of other medical providers and thereby enhance the patient's cooperation with all aspects of care.