Abnormalities of p53 tumour suppressor gene are detected in a diversity of malignancies and play an important role in their pathogenesis. Hypopharyngeal carcinoma is the most morbid among head and neck squamous cell carcinomas because of the high incidence of treatment failures and because a biological marker predictive of the treatment failures remains elusive. The expression of p53 protein in 46 hypopharyngeal squamous cell carcinomas was examined histochemically and p53 immunoreactivity was found in 19 of 46 cases (41.3 per cent). The rate of second primary tumour development was significantly higher in the p53-positive group than in the p53-negative group (p = 0.039), whereas that of tumour recurrence was not significantly different between the two. Moreover, there was no statistically significant difference in either overall or disease-free survival between the p53-positive and -negative groups. These results indicate that although p53 expression significantly correlates with second primary tumour development in patients with hypopharyngeal squamous cell carcinomas, it is not predictive of the clinical outcome.