We have compared the efficacy of granisetron with perphenazine in the prevention of vomiting after tonsillectomy with or without adenoidectomy in children. In a prospective, randomized, double-blind study, 90 paediatric patients, ASA I, aged 4–10 years, received granisetron 40 mg kg−1 or perphenazine 70 mg kg−1 (n=45 each) intravenously immediately after an inhalation induction of anaesthesia. A standard general anaesthetic technique was employed throughout. A complete response, defined as no emesis with no need for another rescue antiemetic, during the first 3 h (0–3 h) after anaesthesia was 87% with granisetron and 78% with perphenazine (P=0.204). The corresponding incidence during the next 21 h (3–24 h) after anaesthesia was 87% and 62% (P=0.007). No clinically serious adverse events were observed in any of the groups. We conclude that granisetron is a better anti-emetic than perphenazine for the long-term prevention of post-operative vomiting in children undergoing general anaesthesia for tonsillectomy.