Infliximab, a tumour necrosis factor (TNF)-alpha antagonist, has shown striking efficacy in the treatment of chronic inflammatory rheumatological diseases such as rheumatoid arthritis and ankylosing spondylitis. However, long-term follow-up studies support that treatment with infliximab is associated with an increased risk of non-Hodgkin lymphoma. So far, few cases of cutaneous lymphoma have been reported in patients receiving TNF-alpha-blocking agents. We report a patient who developed Sézary syndrome 17 months after the onset of infliximab therapy for ankylosing spondylitis. Cutaneous lesions partially remitted following infliximab withdrawal and methotrexate treatment. Although the causal link between infliximab and the emergence of Sézary syndrome is uncertain, the present case raises the need for exhaustive long-term registries of malignancies, including primary cutaneous lymphomas, in patients receiving TNF-alpha-blocking agents.