Abstract Introduction Tuberculous pleural effusions are not always easy to diagnose but the presence of a lymphocyte-rich exudate associated with an increased adenosine deaminase level and a positive skin test result are highly sensitive diagnostic signs. Case presentation We report a case of pleural tuberculosis in a 31-year-old white male patient from Caracas, Venezuela who was negative for human immunodeficiency virus and presented 2 weeks after injecting the anabolic-androgenic steroid nandrolone decanoate, in whom all the tests for tuberculosis were initially negative; an eosinophilic pleural effusion with a low adenosine deaminase level, a negative tuberculin skin test and negative for acid-fast bacilli staining and culture of the pleural fluid. After excluding other causes of eosinophilic pleural effusion malignant pleural effusion was suspected. The patient did not return until 4 months later. The second thoracentesis obtained a pleural fluid suggestive for tuberculosis, with a predominance of lymphocytes, an elevated adenosine deaminase level (51 U/l) and a positive tuberculin skin test. Culture of pleural fragments confirmed pleural tuberculosis. Conclusion This case suggests that the use of an anabolic-androgenic steroid masks the definitive diagnosis of pleural tuberculosis by changing the key diagnostic parameters of the pleural fluid, a finding not previously reported. Available evidence of the effects of anabolic steroids on the immune system also suggests that patients using anabolic-androgenic steroids might be susceptible to developing tuberculosis in either reactivating a latent infection or facilitating development of the disease after a recent infection.