OBJECTIVE The detection of an infraclinical primary by tonsillectomy in case of cervical lymph node of an epidermoid carcinoma with unknown primary after a radical neck dissection, allows avoiding irradiation of the normal larynx. The aim of this study is to quantify the rate of tonsil primary to justify this procedure. METHODS From 1969 to 1992, 87 patients had a tonsillectomy as part of the workup for cervical nodal metastasis of an epidermoid carcinoma with unknown primary. The mean age was 57 years (range: 39-75 years) and the sex ratio was 8.6. Sixty-seven patients had a single cervical adenopathy (17 N1, 30 N2a, 5 N3, 15 Nx), and 20 patients multiple cervical adenopathies (17 N2b, 3 N2c). The treatments included always an irradiation to the node areas (50 Gy), and to the pharyngolarynx in case of normal tonsil (50 Gy), or to the tonsil if it was the primary (50 Gy with a brachytherapy boost of 20-25 Gy). In this last case, the larynx could be protected. RESULTS Tonsillectomy never induced specific complication. Out of 87 patients, 26% had a tonsil primary. There was not specific histological differentiation in this group. In the 67 patients with a single cervical adenopathy, 31% had a tonsil primary (6 N1, 7 N2, 1 N3, 7 Nx). It was a subdigastric adenopathy in 38%, a submandibular in 28% and a midjugulocarotidian in 23%. Among the 17 patients N2b, none had a tonsil primary. In the three patients N2c, two presented a tonsil carcinoma (two subdigastric nodes). CONCLUSIONS Tonsillectomy allows avoiding irradiation of normal larynx in 26% of patients who have a cervical lymph node with unknown primary. It should be performed in case of a single node of the subdigastric, midjugulocarotidian or submandibular area or bilateral subdigastric adenopathies.