The association of rheumatic manifestations with cancer is now well established. There are various rheumatological diseases that can be manifested as paraneoplastic syndromes, i. e. precede or occur simultaneously with different types of tumors, without local evidence of malignancy and regress after effective treatment of the tumor. In fact, the recognition of rheumatic symptoms as the fi rst translation of malignancy is essential for early treatment of the underlying tumor. The authors present a case of a 66 year-old man with no history of relevant disease nor family history of psoriasisor rheumatic diseases, with initial manifestation of chronic oligoarticular frame of the knees with severe systemic infi ammatory component associated with B symptoms, which evolved into symmetric infiammatory polyarthritis and morning stiffness. Analytically, without anemia or lymphopenia, increased infiammatory parameters, hemosedimentation velocity and C-reactive protein; Negative immunological study, including RF and anti-CCP, interpreted as probable seronegative rheumatoid arthritis. Excluded tuberculosis. Initially treated with NSAIDs, corticosteroids and methotrexate (MTX) without much articular benefi t, subsequently conducted infi ltrations and began salazopyrin (SSZ), with some clinical improvement. Onset of oral ulcers, whose biopsy revealed epidermoid carcinoma. Tumor with lymph node metastasis, requiring dissection, radiotherapy and chemotherapy, with clear improvement of the arthritis afterwards. Assumed paraneoplastic arthritis. Disease currently in remission, sporadically medicated only with NSAIDs. The relationship between malignancy and rheumatic manifestations is not simple. It is often diffi cult to identify the underlying tumor if not thinking about it, since the rheumatic paraneoplastic syndromes mimic well the idiopathic situations. On the other hand, the exhaustive search for a neoplasm in the initial assessment of rheumatic diseases is not recommended unless it is a high risk patient. Additionally, paraneoplastic arthritis may have independent natural history of tumors, thus the diagnosis is always a challenge.