OBJECTIVE: To assess the feasibility of implementing a dedicated feeding support team on a postnatal ward and pilot the potential effectiveness and cost-effectiveness of team (proactive) and woman-initiated (reactive) telephone support after discharge. DESIGN: Randomised controlled trial embedded within a before-and-after study. Participatory approach and mixed-method process evaluation. SETTING: A postnatal ward in Scotland. SAMPLE: Women living in disadvantaged areas initiating breast feeding. METHODS: Eligible women were recruited to a before-and-after intervention study, a proportion of whom were independently randomised after hospital discharge to intervention: daily proactive and reactive telephone calls for =14 days or control: reactive telephone calls = day 14. Intention-to-treat analysis compared the randomised groups on cases with complete outcomes at follow-up. MAIN OUTCOME MEASURES: Primary outcome: any breast feeding at 6-8 weeks assessed by a telephone call from a researcher blind to group allocation. Secondary outcomes: exclusive breast feeding, satisfaction with care, NHS costs and cost per additional woman breast feeding. RESULTS: There was no difference in feeding outcomes for women initiating breast feeding before the intervention (n=413) and after (n=388). 69 women were randomised to telephone support: 35 intervention (32 complete cases) and 34 control (26 complete cases). 22 intervention women compared with 12 control women were giving their baby some breast milk (RR 1.49, 95% CI 0.92 to 2.40) and 17 intervention women compared with eight control women were exclusively breast feeding (RR 1.73, 95% CI 0.88 to 3.37) at 6-8 weeks after birth. The incremental cost of providing proactive calls was £87 per additional woman breast feeding and £91 per additional woman exclusively breast feeding at 6-8 weeks; costs were sensitive to service organisation. CONCLUSIONS: Proactive telephone care delivered by a dedicated feeding team shows promise as a cost-effective intervention for improving breastfeeding outcomes. Integrating the FEeding Support Team (FEST) intervention into routine postnatal care was feasible. TRIAL REGISTRATION NUMBER: ISRCTN27207603. The study protocol and final report are available on request.