Active TB affects most commonly the lungs (pulmonary TB), but can affect almost any other organ (extra-pulmonary TB): lungs in 70%, lymph nodes in 15%, peripheral organs (bone, adrenals, uro-genital system) in 15%. Miliary TB (2-3%) is a disseminated form of TB.

The extra-pulmonary and miliary forms of TB are especially common in immune-compromised hosts and in susceptible individuals including: infants, women post–partum, HIV-positive individuals, persons with diabetes mellitus, chronic organ disease, cancer, adrenal insufficiency, and / or on chronic R/ with oral corticoid steroids or immune-suppressive drugs.