A 3-year-old girl was admitted to a children's hospital; subsequently her mother was found to have pulmonary tuberculosis with smear-positive sputum. Of over 400 patients, their families and staff at risk in the hospital, 30 inpatients, three outpatients, two sibling visitors and one staff member became infected. A retrospective cohort study of exposed inpatients identified exposure duration, exposure proximity and primary diagnosis as independent predictors of infection risk. Children with neoplastic disease who were being treated with cytotoxic and immunosuppressive therapy with clotting factors were at a greater risk of developing clinical disease including disseminated infection. Altogether three generations of infected children and adults were diagnosed amongst community and hospital contacts in this extended outbreak. These findings support current recommendations for the follow-up of highly susceptible casual contacts of cases of pulmonary tuberculosis with smear-positive sputa.