The paper reports the case of a 13-year-old female adolescent presenting with persistent fever. She had no other significant symptoms or signs. Laboratory examinations showed mild anemia and elevated C-reactive protein (CRP) and erythrosedimentation rate (ERS). The abdominal ultrasonography revealed para-aortic lymphadenopathy that was confirmed by magnetic resonance imaging (MRI) and positron emission tomography-computed tomography (PET/CT) that showed no other locations. The patient underwent laparoscopic excision but complete removal was not possible due to the position of the mass. The histological exam documented unicentric Castleman's disease. After surgery a clinical improvement was assisted but with persistence of very high CPR, ERS and serum amyloid. According to guidelines, she was treated with tocilizumab achieving complete remission of indices of inflammation. In the case with symptomatic unresectable unicentric Castleman's disease treatment with anti-IL-6 agents should be considered.