Pulmonary Kaposi sarcoma (KS) is a potentially fatal complication of AIDS/HIV infection. With the development of highly active antiretroviral therapy (HAART), the morbidity and mortality associated with AIDS/HIV have decreased significantly. However, a small number of patients started on HAART develop a severe inflammatory response to preexisting pathogens or antigens, known as immune reconstitution inflammatory syndrome. We describe a case of rapidly progressive pulmonary KS in a patient with AIDS who was recently restarted on HAART and provides a review of immune reconstitution inflammatory syndrome and its association with KS.