Vomiting and nausea are the most distressing side-effects of cancer chemotherapy. With standard antiemetic regimens (e.g. metoclopramide based combinations) sufficient antiemetic control is achieved in 50-70% of cisplatin treated patients. Ondansetron, a selective 5-HT3-receptor antagonist has shown efficacy in cisplatin-induced emesis. In the present study, we evaluated the safety and efficacy of ondansetron in cisplatin pretreated patients who had suffered from severe emesis in spite of antiemetic prophylaxis. Complete antiemetic control was reached in 43.5% on the day of treatment and in 27.2% of the patients regarding a worst day analysis. 25% of the patients suffered from severe cisplatin-induced emesis (greater than 5 emetic episodes per 24 h). We try to characterise risk-factors for cisplatin-induced emesis by performing a multivariate analysis. Sex, cisplatin dose, and combination therapy with cisplatin plus anthracyclines seem to be independent risk-factors for vomiting on day 1 and on worst day. Delayed emesis occurred less often when sufficient antiemetic protection from acute vomiting had been obtained. Female sex, cisplatin dose and recurrent disease seem to influence the probability for occurrence of delayed vomiting.