The charts of 5,019 previously untreated patients with squamous cell carcinoma of the upper respiratory and digestive tracts who completed treatment for cure from January 1948 through August 1973, were reviewed. These patients had no evidence of distant metastases when initially evaluated. Five hundred and forty-six patients developed clinical evidence of distant metastases. The overall incidence of distant metastases was 10.9%, varying from 3.1% for vocal cord cancers to 28.1% for cancer of the nasopharynx. The lungs and bones were the most common first sites of metastases, accounting for 52% and 20.3% respectively, whereas metastases to the mediastinum (2.9%) were rare. Forty-eight percent of the metastases were detected within nine months after treatment and 80% were detected within two years. The rate of distant metastases increased with the stage (2% for Stage I to 19.5% for Stage IV). The rate also increased with the T and N classification; however, the N stage had greater influence on the rate of metastases than the T stage. The incidence of distant metastases was significantly higher when there was a recurrence above the clavicles (16.7%) than when there was no recurrence (7.9%, less than 0.001). In patients whose primary lesion was treated by radiotherapy or surgery alone, the incidence was essentialy the same. Patients receiving postoperative irradiation had double the incidence of the preoperative group (20.1% vs 9.9%--p less than .005); however, the sequence of modalities was not randomized.