Background The efficacies of granisetron plus dexamethasone and dexamethasone alone in controlling delayed nausea and vomiting after cisplatin chemotherapy (≥69 mg/m2) were compared in a multicentre, double-blind, placebo-controlled comparative study. Patients and methods In all, 654 patients (of whom 619 were evaluable) received prophylactic granisetron plus dexamethasone before chemotherapy on day 0; on day 1 complete responders and non-responders were randomized separately to receive dexamethasone, 8 mg b.d. p.o., with either granisetron, 1 mg b.d. p.o., or matching placebo for six days. Results Over days 1–6 the complete response rates were 54.5% (dexamethasone group) and 52.1% (dexamethasone plus granisetron group). Response rates were higher over days 4–6 (71.8% and 70.7%, respectively) than over days 1–3 (60.4% and 57.9%, respectively). Significantly more patients who responded to antiemetic treatment during day 0 were responders over days 1–6 (63% vs. 17% P < 0.001). No other treatment-related differences were found. Adverse events tended to be minor, with constipation and headache the most common. Overall, there were no significant differences in the safety profiles of the two regimens, but constipation and abdominal pain were significantly more common in the dexamethasone plus granisetron group. Conclusions Granisetron plus dexamethasone did not appear to confer additional benefit over use of dexamethasone alone in controlling delayed nausea and vomiting following cisplatin chemotherapy. Control of acute nausea and vomiting, however, appeared to be an important factor influencing delayed nausea and vomiting.