Tuberculosis presenting as monoarticular involvement in immunocompetent patients is rare. Here, we report a Sri Lankan patient presenting with ankle swelling due to tuberculosis with no other extrapulmonary or pulmonary involvement. Magnetic resonance imaging showed destruction of articular cartilage of the ankle joint with chronic inflammation of the subtalar joint. The diagnosis was confirmed by synovial tissue culture which was positive for Mycobacterium tuberculosis. The patient recovered uneventfully with anti-tuberculosis treatment. Therefore, a high degree of suspicion is necessary to diagnose extrapulmonary tuberculosis when patients are presenting with atypical monoarthritis.