1. ACC (adenoid cystic carcinoma; cylindroma) of the airways is a very rare tumor in thoracic surgery.

2. In the differential diagnosis the intercalated duct carcinomas must be distinguished from acinic cell tumors, cylindromas (adenoid cystic carcinomas) and from mucoepidermoid tumors.

3. Adenoid cystic carcinoma or Cylindroma is a malignant tumor that originates most often from both minor and major salivary glands.

4. The insidious character of the acinic cell tumors (i. e. the acinic cell adenocarcinoma) and of the cylindroma (i. e. the adenoid cystic carcinoma) ranges from a considerable to a high degree.

5. Since myoepithelial cells do not occur, the basal-cell adenoma can easily be separated from salivary gland tumors containing myoepithelial cells, i.e., from the pleomorphic adenoma (socalled mixed tumor), the adenoid-cystic carcinoma (cylindroma), and the salivary duct carcinoma.