Castleman's disease is a rare lymphoproliferative syndrome involving several anatomical and clinical entities. We report two cases of Castleman's disease in patients with spondyloarthritis (with and without psoriasis) treated with Tumor Necrosis Factor-alpha blockers. During follow-up, imaging examinations, carried out for disease assessment, fortuitously revealed a pelvic mass close to the psoas or an atypical cervical adenopathy. Both lesions were in moderate hypermetabolism on Positron emission tomography–computed tomography. After surgical excision and histological analysis, Castleman's disease was diagnosed without signs of malignancy. To the best of our knowledge, these are the first cases of Castleman's disease diagnosed in a context of spondyloarthritis treated with Tumor Necrosis Factor-alpha blockers. The relationship between these two pathologies and the link with Tumor Necrosis Factor-alpha blockers agents has not been explored in the literature until now.