Minute squamous cell carcinoma arising in the wall of a congenital lung cyst. A case of minute squamous cell carcinoma arising in a congenital lung cyst is reported. Two aspects of this case were notable. First, we were able to make the diagnosis of squamous cell carcinoma by bronchial lavage at an early stage. Second, to our knowledge, this is the first case of probable de novo origin of squamous cell carcinoma in a congenital lung cyst. 