Among postoperative pleural space problems after pulmonary resections, it is more difficult and troublesome to manage this space after left upper lobectomy in patients with chronic obstructive pulmonary disease (COPD). We performed a retrospective study focusing on the elevation of ipsilateral hemidiaphragm of the 36 patients with or without COPD after left upper lobectomies, by measuring diaphragmatic dome length (DDL) with a plain posteroanterior roentgenogram. They were divided into two groups: group I (forced expiratory volume in 1 s (FEV1) % predicted < 70%, n = 5); and group II (FEV1) % predicted > or = 70%, n = 31). Of each group, we investigated the trend of both left and right DDLs perioperatively, calculating DDL index (DDL divided by height, DDLI), and also analyzed several perioperative parameters. The trend of left DDLI after surgery was different in the two groups (P=0.012). In group I, left DDLI became larger gradually in proportion to the postoperative weeks, while in group II it became the largest 2 weeks after surgery and decreased gradually. Left DDLI in group I was smaller than that in group II 2 weeks after surgery (P=0.007). We found that the diaphragm of COPD patients does not elongate easily after left upper lobectomy.