A 60-year-old man with lymphoma completed chemotherapy on October 21, 2016, with complete remission. He then received rituximab maintenance therapy. Since March 2017, he has had progressive fatigue, myalgias, rash, weight loss, diarrhea, and recurrent low-grade fever. Subsequent bone marrow biopsy and FDG PET/CT demonstrated no active lymphoma. An 111In–white blood cell scan showed abnormal tracer uptake on 20-hour postinjection, but not on 3-hour postinjection images, including innumerable skeleton muscle foci, multiple cutaneous foci, and persistent diffuse increased uptake in the lungs. Diagnosis of adult-onset Still disease was made accordingly. The patient's cytopenia was deemed a chemotherapy-related adverse effect.