Active tuberculosis (TB) infection including asymptomatic and extrapulmonary disease may be detected with 18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). This report highlights the promising role of FDG-PET/CT for evaluation of TB in high-risk, immunocompromised patients with cancer. PET/CT performed for cancer evaluation may detect asymptomatic infection and guide definitive diagnosis. It may also be a useful tool in the assessment of latent TB, to exclude active disease prior to treatment. PET/CT has potential for monitoring response to anti-tuberculosis treatment. Metabolic response may indicate clinical response and guide duration of anti-microbial therapy.