Objectives: Form discordance of cavity walls (FDCW) and form concordance of cavity walls (FCCW) in multislice spiral CT (MSCT) were investigated to determine their value in differentiating between peripheral lung cancer cavities and single pulmonary tuberculous thick-walled cavities. An assessment of the role of multiplanar reconstruction (MPR) in detecting FDCW and FCCW was also performed. Methods: MSCT cross-sectional images of 116 consecutive cases (including 60 cases with available MPR images) with peripheral lung cancer cavities and 118 consecutive cases (including 62 cases with available MPR images) with single pulmonary tuberculous thick-walled cavities (wall thickness .3 mm) were retrospectively analysed. According to the characteristics of cavitary internal and external walls on MSCT, these cavities were divided into two types (FDCW and FCCW). FDCW was further divided into three subtypes (FDCW-I, FDCW-II and FDCW-III); FCCW was further divided into two subtypes (FCCW-I and FCCW-II). Results: On the cross-sectional and MPR images, the total detection rate of FDCW-I and FDCW-III in peripheral lung cancer cavities was 76.7% (89/116) and 93.3% (56/60), respectively, whereas the total detection rate of FCCW-I and FCCW-II in single pulmonary tuberculous thick-walled cavities was 75.4% (89/118) and 91.9% (57/62), respectively. Conclusions: FDCW-I, FDCW-III, FCCW-I and FCCW-II were valuable in differentiating between peripheral lung cancer cavities and single pulmonary tuberculous thick-walled cavities. MPR could improve the detection of FDCW-I and FDCW-III in peripheral lung cancer cavities and FCCW-I and FCCW-II in single pulmonary tuberculous thick-walled cavities. Cavities are frequent image findings in a variety of pulmonary diseases. Many of these diseases, including both lung cancer and pulmonary tuberculosis, can form a cavity during their course [1][2][3]. The cavities formed during these two particular diseases are difficult to distinguish [1,4,5], particularly in the case of peripheral lung cancer cavities and single pulmonary tuberculous thick-walled cavities. Although numerous studies have been conducted in this area, there is still no pertinent literature on the differential diagnostic value of form concordance or discordance of cavitary internal and external walls obtained from multislice spiral CT (MSCT). The aim of this study was to analyse MSCT manifestations of form discordance of cavity walls (FDCW) and form concordance of cavity walls (FCCW) to ascertain their value in differentiating between peripheral lung cancer cavities and single pulmonary tuberculous thick-walled cavities. In addition, the role of multiplanar reconstruction (MPR) in detecting FDCW and FCCW is assessed. Between May 2006 and June 2008, 116 consecutive cases of peripheral lung cancer cavities confirmed using pathological specimens obtained through surgical resection (n580) or CT-guided transthoracic needle aspiration (n536) were retrospectively analysed. The patients ranged in age from 36 to 76 years (mean age, 58 years...