Gastrointestinal toxicity, including oral mucositis, is a frequent complication of intensive combination chemotherapy for acute myeloid leukaemia (AML) and contributes substantially to treatment-related mortality. We conducted a placebo-controlled randomized trial to evaluate the efficacy of palifermin (keratinocyte growth factor), given at 60 μg/kg per daily IV for 3 d before and after chemotherapy, for mucosal protection in adult patients with previously untreated AML receiving induction therapy with idarubicin, high-dose cytarabine and etoposide. Among 155 randomized patients, there was no statistically significant difference in the rate of grade 3 and 4 oral mucositis (primary study endpoint) between the two treatment arms (three in palifermin arm (4%), 8 in placebo arm (10%; P = 0·21); however, when considering the severity of oral mucositis (World Health Organization grade 0-4), there was evidence of reduced rates of higher grades of oral mucositis in the palifermin arm (P = 0·0007, test for trend). There was a statistically significantly lower rate of grades 3 and 4 gastrointestinal adverse events in the palifermin arm (21% vs. 44% in placebo arm; P = 0·003), mainly due to a reduction in severe diarrhoea (8% palifermin, 26% placebo; P = 0·01). Palifermin has activity as a mucosal protectant in AML patients receiving intensive chemotherapy. This trial is registered at ACTRN012605000095662.