East Asian case-control studies have shown a strong relationship between alcohol consumption combined with inactive heterozygous aldehyde dehydrogenase-2 (ALDH2*1/*2) and the development of squamous cell carcinoma (SCC), especially multiple SCC, of the upper aerodigestive tract (UADT). This study aimed to identify determinants of the development of metachronous SCC in the UADT in alcoholics with esophageal SCC. Follow-up endoscopic examinations were carried out 4-160 months (median, 41 months) after initial diagnosis in 110 Japanese alcoholic men with esophageal SCC diagnosed by screening using endoscopy combined with oropharyngolaryngeal inspection and esophageal iodine staining. ALDH2*1/*2 was significantly associated with the presence of multiple primary intraesophageal SCC at the time of initial diagnosis. Metachronous primary SCC of the esophagus was diagnosed in 29 of the 81 patients whose initial esophageal SCC was treated by endoscopic mucosal resection alone, and metachronous primary SCC of the oropharyngolarynx was diagnosed in 23 of the 99 patients without synchronous primary SCC of the oropharyngolarynx at the time of initial diagnosis. The risks of metachronous esophageal SCC and oropharyngolaryngeal SCC were significantly higher in ALDH2*1/*2 heterozygotes than in ALDH2*1/*1 homozygotes (age-adjusted and alcohol-adjusted hazard ratio = 3.38 [95% confidence interval: 1.45-7.85] and 4.27 [1.42-12.89], respectively), and in patients with multiple intraesophageal SCC at the time of initial diagnosis than in patients with a solitary intraesophageal SCC (3.09 [1.41-6.78] and 3.25 [1.41-7.47], respectively). ALDH2*1/*2 and multiple synchronous intraesophageal SCC were found to be predictors of metachronous SCC in the UADT in this population.