We have reviewed the results from 15 tuberculosis treatment trials initiated by the British Medical Research Council between 1970 and 1983 in Africa and East Asia. Of 574 relapses, 447 (78%) occurred within 6 months of stopping treatment and 525 (91%) within 12 months. We suggest that investigators should consider terminating follow-up after the last enrolled patient completes 6 months following treatment, while continuing to follow patients enrolled earlier until that time. Compared to following all patients to 24 months, the total trial duration could be reduced by 18 months, with no increase in patient numbers in a non-inferiority design.