We retrospectively reviewed the chart records at the Veterans General Hospital-Taipei for the period between January 1985 and December 1994 to examine the temporal relationship between cancers of the lung and upper aerodigestive tract. A total of 56 patients (54 males, 2 females) with histocytologically proven double primary cancers, with either lung cancer or upper aerodigestive tract cancers appearing first, were found. Squamous cell carcinoma was the most frequent histologic type of lung cancer (squamous 57%, adenocarcinoma 27%, poorly differentiated carcinoma 9%, small cell lung cancer 7%). The incidence of lung cancer patients with upper aerodigestive tract cancer was 0.9% (56/6412). There was no significant difference in the occurrence of upper aerodigestive tract cancer between non-small cell and small cell lung cancer (P > 0.05). However, the incidence of squamous cell lung cancer with upper aerodigestive tract cancer was higher than that of non-squamous cell lung cancer (P < 0.05). With regard to the location of lung cancer, the right lung was more commonly affected than the left (P < 0.001). The locations of upper aerodigestive tract cancers in these lung cancer patients were as follows: larynx 24, nasopharynx 11, esophagus 10, hypopharynx 4, pharyngeal tonsils 2, oral cavity 5. Most upper aerodigestive tract cancers were diagnosed before lung cancer (36/56, 64%), and lung cancer was diagnosed within 3 years in more than half of cases after the diagnosis of upper aerodigestive tract cancer (58.3%). Most lung cancers that preceded upper aerodigestive tract cancer were at an early stage at diagnosis (stage I 4, stage Illa 1), whereas the others, appearing either synchronously or after the diagnosis of upper aerodigestive tract cancer, were mostly at the late stage. There was no difference in survival between lung cancer patients with upper aerodigestive tract cancer and those without (P > 0.05).