A 41-year-old man presented with chronic cough and chest pain. Laboratory tests revealed anemia, inflammation, hypoalbuminemia, polyclonal hypergammaglobulinemia, and elevated interleukin-6 levels. Computed tomography revealed diffuse bilateral pulmonary nodules and multicentric lymphadenopathy. Histopathology of the pulmonary nodule resembled pulmonary hyalinizing granuloma (PHG), whereas lymph node histopathology was consistent with idiopathic multicentric Castleman disease (iMCD). The patient was diagnosed with iMCD involving PHG-like pulmonary nodules. Little is known about the association between these two diseases, and the present case provides insights regarding the relationship between PHG and iMCD.