The association between cisplatin treatment and diabetes mellitus was analyzed retrospectively in 219 patients with locally advanced squamous cell head and neck cancer treated in two consecutive trials with cisplatin-based induction chemotherapy. It was found that 11 patients (5%) developed diabetes mellitus during the treatment period, two cases presenting as hyperosmolar coma. The literature contains only sporadic descriptions of cases of hyperosmolar coma related to cisplatin chemotherapy. The present study was initiated owing to a case of hyperosmolar coma observed by us. We suggest that glycemia levels in patients receiving chemotherapy with a cisplatin-based regimen should be monitored regularly.