In patients with hematologic disorders, cellular immunity may be suppressed by the disease itself or by treatment with adrenal corticosteroids, immunosuppressants, or anticancer agents. Miliary tuberculosis developing in such compromised hosts is cryptic, and thus its diagnosis is difficult to make. Miliary tuberculosis will be fatal if it cannot be detected. Therefore, the possibility of mycobacterial infection should always be kept in mind when treating patients with hematologic disorders. However, such patients often have a poor prognosis, even if they have already been diagnosed with miliary tuberculosis. Prophylactic medication has been proved to be effective against mycobacterial infection with hematologic disorders. Thus, the importance of prophylactic medication should be emphasized.