Exposure to TB was quantified by screening human immunodeficiency virus (HIV) exposed infants aged 3-4 months for an isoniazid prophylaxis study where tuberculosis (TB) exposure excluded enrolment. Seventy-seven (10.1%, 95%CI 8.0-12.4) of 766 infants had contact with a TB source case. Nurses and lay counsellors identified 52 infants during pre-screening and doctors identified 25 during formal screening. High exposure may contribute to high rates of TB in HIV-exposed infants. Programs to prevent mother-to-child transmission of HIV offer an important opportunity to screen for TB. In-depth assessment is required for evaluating TB exposure.