A case-control study was carried out in 44 non-private hospitals in Malawi which register and treat patients with tuberculosis (TB), to determine whether households of index TB patients had an increased frequency of TB compared with households where no TB had been diagnosed. Interviews were conducted in 770 smear-positive PTB patients and 918 control patients from antenatal, orthopaedic or surgical wards. TB patients and controls came from households which were similar in terms of type of house, household cash income and family size. In the previous 12 months, 52 (7%) TB patients had household members who developed TB compared with 11 (1%) control patients (OR 5.97, 95%CI 2.99-12.21). Of 2766 household members of TB patients, 56 had developed TB in the previous 12 months (frequency = 2024/100,000), which was significantly higher than the 11/4121 household members of control patients (frequency = 343/100,000, P < 0.001). There is a higher frequency of TB in households of index TB patients.