A 28-year-old man treated with the antitumour necrosis factor α (TNFα) monoclonal antibody infliximab for Crohn's disease developed pulmonary tuberculosis (TB), despite testing negative for latent TB prior to treatment. On starting anti-TB treatment and withdrawal of the anti-TNFα therapy, he deteriorated both clinically and radiologically. He was diagnosed with a flare of Crohn's disease, and immune reconstitution inflammatory syndrome (IRIS) in his right upper lobe and mediastinal lymph nodes, and commenced on oral prednisolone. Anti-TNFα therapy was re-introduced, and prednisolone weaned, following 4 months of anti-TB treatment without complication. He made a full recovery from TB, although his Crohn's symptoms continue to be troublesome. There has been no reactivation of TB to date, after 2 years follow-up.