Decortication is widely performed for empyema, but the effectiveness in achieving lung re-expansion has never been formally reported. The aim of this study is to quantify the degree of lung re-expansion in comparison to that achieved naturally after debridement alone. A retrospective review of patients who underwent either decortication or debridement for empyema between 2007 and 2009. The change of the cavity size with time were standardized and recorded before, immediately after surgery and on follow-up. Of 25 patients who underwent surgical management of empyema, 16 (64%) underwent debridement alone and nine (36%) underwent decortication. The mean age (standard deviation) was 58 (19) years and 15 (60%) were male. On radiological follow-up at a median [interquartile range (IQR)] of 45 (36-116) days, further reduction of 36% and 34% was achieved leaving 27% and 12% of the original cavity size in the debridement and decortication groups, respectively. Procedure (debridement or decortication) was not associated with any difference to the eventual follow-up cavity size (P = 0.937). Similar follow-up results were achieved by debridement alone without decortication in patients presenting with empyema, despite the presence of an underlying trapped lung.