SETTING: All 44 non-private hospitals in Malawi treating pulmonary tuberculosis (PTB) patients with an oral regimen (0.5RHZE/1.5R3H3Z3E3/6HE). OBJECTIVES: In new smear-positive PTB patients, to determine whether: 1) numbers of tablets were correctly prescribed according to pre-treatment weights, and 2) medication dosages were adequate, too low or too high. DESIGN: Retrospective review of TB registers and TB treatment cards for patients registered with new smear-positive PTB between 1 October and 31 December 2001. RESULTS: Of 1970 patients aged > or = 15 years, 1211 (62%) had treatment cards and pre-treatment weights. Incorrect prescriptions were given to 88 (7%), and many of these received dosages of anti-tuberculosis drugs that were too high or too low. For those receiving correct prescriptions, daily treatment in the initial and continuation phases was generally associated with adequate dosages of drugs. However, in the initial intermittent phase, between 3% and 40% of patients received anti-tuberculosis drug dosages that were too low. CONCLUSION: A small percentage of patients receive incorrect prescriptions, which can be resolved by training and supervision. In those receiving correct prescriptions, intermittent treatment provides dosages that are sometimes too low. Weight bands for intermittent treatment should be re-examined.