Understanding the ways in which atelectasis contributes to the clinical course decline in patients with primary lung cancers becomes paramount when considering indications for airway prosthesis application or stenting. A series of 328 patients with advanced primary lung cancer consisting of ad-enocarcinomas and squamous and small-cell lung carcinomas were screened retrospectively for instances when atelectasis occurred at least once during each patient's entire clinical course. Of these 328 patients, 64 had one or more episodes of atelectasis during their entire clinical course and comprised 69 atelectatic events including relapsed atelectasis. Atelectasis occurred more frequently in patients with squamous cell carcinoma in the earlier clinical stages than in patients with adenocarcinoma. However, patients with squamous cell carcinoma were associated with a higher incidence of pulmonary infection caused by atelectasis than patients with adenocarcinoma or small-cell carcinoma. In addition, patients having squamous cell carcinoma and obstructive pneumonia with atelectasis showed a remarkably high mortality rate. In contrast, atelectasis alone rarely contributed to obstructive pneumonia or clinical deterioration in patients with adenocarcinoma or small-cell carcinoma. Therefore, intervention such as stenting may be specifically advised in clinical situations involving squamous cell carcinoma-associated atelectasis.