The expression and prognostic significance of the c-erbB-2 oncogene product was studied in 55 cases of childhood medulloblastoma. Forty-six of the 55 tumours (83.6%) expressed the c-erbB-2 product. The percentage of tumour cells expressing the c-erbB-2 product proved to be a significant indicator of patient outcome when analysed as both a categorical and a continuous variable. As a categorical variable, patients with more than 50% positive tumour cells had a significantly worse survival, with only 10% alive at 10 years vs 48% for those with less than 50% positive tumour cells (log rank P = 0.0049). To demonstrate that this observed prognostic significance was both independent and not a result of 'data-driven' categorisation, it was also entered into the Cox model as a continuous variable. Prognostic significance was retained in P = 0.038.