OBJECTIVE To assess the efficacy of corticosteroids in the treatment of severe hyperemesis gravidarum refractory to conventional management. METHODS Multicentre, double-blind, randomised, placebo-controlled trial. METHODS Inpatient gynaecology wards in eight collaborating centres. METHODS Twenty-five women with severe hyperemesis of which 24 completed the one- week study period. METHODS Twenty-five women were randomised to receive either 40 mg prednisolone daily in two divided oral doses, or equivalent placebo tablets. If, after three days, a woman was still vomiting, medication was changed to the equivalent intravenous alternative (hydrocortisone 100 mg twice daily or normal saline injections) METHODS Frequency of vomiting and the dependence on intravenous fluid replacement therapy after one week of treatment. RESULTS There was a non-significant trend towards improved nausea and vomiting and reduced dependence on intravenous fluids. However, steroid therapy led to an improved sense of wellbeing (P = 0.021), improved appetite (P = 0.039) and increased weight gain (P = 0.025) compared with placebo. There was no difference in pregnancy outcome between the treatment and placebo groups. CONCLUSIONS This study supports a beneficial role for steroids in severe hyperemesis, but did not validate the hypothesis that they lead to rapid and complete remission of symptoms. The study was not large enough to demonstrate a significant improvement in the primary outcome measures.