Relapsing polychondritis and Sweet's syndrome are rare systemic inflammatory conditions. The authors present a patient who developed Sweet's syndrome 1 week after adalimumab therapy for refractory relapsing polychondritis. Coexistent relapsing polychondritis and Sweet's syndrome is rare, however, is likely to represent a true disease association and signifies a high risk of myelodysplasia. Antitumour necrosis factor α (TNFα) therapy is a treatment option in both relapsing polychondritis and Sweet's syndrome, and switching anti-TNFα agents may be feasible in the event of adverse reaction.