Immunocompromising conditions include both those acquired at birth (ex: SCID, Wiscott-Aldrich, hyperimmunoglobulin E syndrome) and those that acquired later in life (CVID). Commonly encountered immunocompromised adult patient groups include those with AIDS at risk for opportunistic infections, and those on chemotherapy/biolologic agents for treatment of malignancy or rheumatic diseases. Infections in patients who have undergone solid organ or bone marrow transplant are life-threatening and as more transplants are being performed, it is even more vital that physicians are aware of common complications including infection. We will review some case examples.