A long-term follow-up study was carried out to assess ototoxicity in children who had been treated for a malignant tumour with "standard dose" cisplatin (60-100 mg/m2 per course), and were at least 2 years from stopping treatment. The median age at diagnosis was 2 years 2 months (range 1 month to 13.5 years). On the basis of hearing assessment by pure-tone audiometry, a practical grading system of hearing loss from 0 to 4 is proposed. Moderate to severe high-frequency hearing loss (grade 2-4) was found in half the children and 10 require appropriate hearing aids. The risk of developing ototoxicity increased significantly with the cumulative cisplatin dose (P = 0.027), although there was considerable individual susceptibility. Serial follow-up testing, to a median of 4 years after completion of cisplatin treatment, showed no recovery of hearing in any of these children. We suggest careful monitoring of young children by a consultant audiological physician throughout treatment with cisplatin, particularly when doses of 400 mg/m2 and over have been reached. Alternative chemotherapy should be discussed if grade 2 ototoxicity develops.