A 35-year-old woman was admitted to our hospital complaining of a left cervical mass. Contrast-enhanced computed tomography (CT) showed multiple enlarged lymph nodes in the cervical, mediastinal, hilar, intra-abdominal, and inguinal areas, and a pulmonary mass in the left upper lobe. Biopsy specimens were obtained from the left inguinal lymph nodes and the left pulmonary mass, which confirmed the diagnosis of follicular lymphoma and sarcoidosis, respectively. The patient subsequently underwent bendamustine plus rituximab as a first-line treatment for lymphoma; however, the left pulmonary mass and multiple lymph nodes, including the left cervical lymph nodes, became enlarged. Another biopsy was performed on the left cervical lymph nodes. It revealed a non-caseating epithelioid granuloma, which was suggestive of an exacerbation of sarcoidosis, but not of lymphoma. During a two-year follow-up after the discontinuation of chemotherapy the enlarged lymph nodes and pulmonary mass have started to decrease in size without any treatment.