The object of this investigation was to evaluate in the long-term the risk of malignancy occurring in the larynx of patients with dysplasia in the laryngeal epithelium. Over an 8-year period, 1974-82, 170 patients underwent microlaryngoscopic examination of the larynx including biopsy, showing hyperplasia and/or keratosis with or without dysplasia in the laryngeal epithelium. Of these, 147 patients were examined, on an average, 5 years and 4 months later. All histological specimens were reviewed by the same pathologist. Of the patients initially showing mild dysplasia, 7.8% developed aggravation while 55.6% of the patients displaying moderate dysplasia had developed severe dysplasia or carcinoma. 93.2% were smokers. It is concluded that all patients with atypia in the laryngeal epithelium should be observed at regular intervals, but special attention should be given to patients showing moderate dysplasia or worse.