To investigate the relationship between esophageal dysplasia and the development of both esophageal cancer (EC) and head and neck cancer (HNC), a clinicopathological study was performed in 113 patients with EC who underwent esophagectomy without any preoperative treatment. The incidence of dysplastic lesions in the resected esophagus was determined by a whole-organ stepwise cutting method. Synchronous or metachronous primary HNC was present in 25 patients, all of whom were male (Group A) and absent in both 70 male patients (Group B) and 18 female patients. A total of 628 dysplastic lesions were found in 79 patients; 67 of them were graded as carcinoma in situ (CIS) in 26 patients, 44 as severe dysplasia (SD) in 16 patients, 182 as moderate dysplasia (MOD) in 59 patients, and 335 as mild dysplasia (MID) in 58 patients. The incidence of CIS, SD and MOD was low in females, slightly increased in Group B, and markedly increased in Group A, and the differences between Group A and Group B and between Group A and females were statistically significant. There was a sex difference in smoking and alcohol consumption, only a few smokers or drinkers being female, whereas there was no significant difference between Groups A and B in smoking and alcohol consumption. CIS, SD or MOD in the esophagus appear to be closely related to both EC and HNC, and patients with EC associated with CIS, SD or MOD are at increased risk of developing HNC.