An HIV-infected man in his 30s was transferred to our hospital after the discontinuation of antiretroviral therapy (ART) for 4 years. An intraoral tumor was identified, and a biopsy was performed. The diagnosis was Kaposi's sarcoma (KS) and disseminated lesions were detected in his respiratory tract and both lungs on computed tomography (CT) and 2-[18F] fluoro-2-deoxy-D-glucose positron-emission tomography (FDG/PET) imaging with increasing standardized uptake volume (SUV: max 7.4). On the 7th day, he was intubated to maintain his airway, then antiretroviral therapy and chemotherapy with pegylated liposomal doxorubicin were immediately initiated. After a period of remission, pulmonary lesions were detected again. We regarded them as a manifestation of immune reconstitution inflammatory syndrome (IRIS) and gave him short term corticosteroids. The lesions were then successfully controlled without additional chemotherapy. This case suggests that early induction of ART and intensive care can result in the survival of patients with KS having serious stenosis of the respiratory tract. Furthermore, this presenting case suggested that the use of corticosteroids could be a candidate to control IRIS even in patients with Kaposi's sarcoma.