Multiple primary lesions were initially thought to be rare occurrences; however, recent numerous series show the incidence to vary from 1% to 11%. These reports generally refer to lesions that develop subsequently to diagnosis and treatment of the initial lesion, and the results of these studies reflect improved follow-up, treatment, and possibly a true increase in frequency. In the search for synchronously developing primary lesions, it was decided to perform panendoscopies on all cases of cancer of the upper aerodigestive tract, irrespective of size or situation or whether they were amenable to evaluation under local anesthesia. These panendoscopies were performed on 162 consecutive cases with a diagnosis of 15 synchronous second primary lesions, ie, an incidence of 9.2%. For this reason, as much time and effort as possible should be devoted to detecting the synchronous second primary lesion as the later developing lesion, and panendoscopy has proved invaluable in achieving this.