INTRODUCTION Cutaneous tuberculosis (CT) is rare in industrialized countries. Given the clinicopathological polymorphism and the difficulty of isolating the pathogen, diagnosis can be difficult. The condition may be associated with other known locations of the disease or in rare cases, it may be a tell-tale sign, as in our case, in which leg ulcers revealed paucisymptomatic disseminated tuberculosis. OBSERVATION A 67-year-old man was referred for rapidly extensive ulcers of the right leg contiguous to debilitating arthritis of the knee of unknown aetiology for 18 months. Earlier investigations revealed thymoma and a pulmonary nodule considered to be sarcoidosis. A skin biopsy showed a granulomatous eosinophilic-rich infiltrate and vasculitis of the small vessels. Screening of the skin sample and gastric aspirate for Koch Bacillus (BK) was negative. A diagnosis of sarcoidosis was made. A positive QuantiFERON test eventually led to the correct diagnosis. On further testing of bronchoalveolar fluid and a synovial biopsy, culture for Mycobacterium tuberculosis (MT) was positive. The PET scan showed high metabolism in the prostate, bone, spleen, liver, nodes and heart. The quad- and then dual-antibiotic antitubercular therapies produced a rapid improvement but treatment was continued over 12 months, given the persistence of high metabolism on PET-CT scan and the low blood rifampicin concentration. DISCUSSION A CT should be considered in the presence of giant-cell granulomas, even in the absence of caseous necrosis, and where both direct examination and culture for the skin are negative. Our case also underlines the importance of an extensive workup to rule out disseminated disease even if the patient is not symptomatic.