OBJECTIVE: to evaluate the effects of an extended midwifery support (EMS) programme on the proportion of women who breast feed fully to six months. DESIGN: randomised controlled trial. SETTING: large public teaching hospital in Australia. PARTICIPANTS: 849 women who had given birth to a healthy, term, singleton baby and who wished to breast feed. INTERVENTION: participants were allocated at random to EMS, in which they were offered a one-to-one postnatal educational session and weekly home visits with additional telephone contact by a midwife until their baby was six weeks old; or standard postnatal midwifery support (SMS). Participants were stratified for parity and tertiary education. MEASUREMENTS: the main outcome measures were prevalence of full and any breast feeding at six months postpartum. FINDINGS: there was no difference between the groups at six months postpartum for either full breast feeding [EMS 43.3% versus SMS 42.5%, relative risk (RR) 1.02, 95% confidence interval (CI) 0.87-1.19] or any breast feeding (EMS 63.9% versus SMS 67.9%, RR 0.94, 95%CI 0.85-1.04). CONCLUSIONS: the EMS programme did not succeed in improving breast-feeding rates in a setting where there was high initiation of breast feeding. Breast-feeding rates were high but still fell short of national goals. IMPLICATIONS FOR PRACTICE: continuing research of programmes designed to promote breast feeding is required in view of the advantages of breast feeding for all mothers and babies.