In this report, we describe treatment outcomes in the first case of a patient with tumor necrosis factor receptor–associated periodic syndrome (TRAPS) treated with the anti–interleukin-6 (anti–IL-6) receptor monoclonal antibody tocilizumab. Since IL-6 levels are elevated in TRAPS, we hypothesized that tocilizumab might be effective. The patient, a 52-year-old man with lifelong TRAPS in whom treatment with etanercept and anakinra had failed, was administered tocilizumab for 6 months, and the therapeutic response was assessed by measurement of monocyte CD16 expression and cytokine levels. Following treatment, the evolving acute attack was aborted and further attacks of TRAPS were prevented. The patient did not require corticosteroids and showed significant clinical improvement in scores for pain, stiffness, and well-being. Moreover, the acute-phase response diminished significantly with treatment. Monocyte CD16 expression was reduced and the numbers of circulating CD14+CD16+ and CD14++CD16− monocytes were transiently decreased. However, cytokine levels were not reduced. This case supports the notion of a prominent role for IL-6 in mediating the inflammatory attacks in TRAPS, but blockade of IL-6 did not affect the underlying pathogenesis. These preliminary findings require confirmation.