The aim of the present study was to investigate the difference in doubling time between squamous cell carcinoma (SCC) and adenocarcinoma of solid pulmonary cancer using three-dimensional volumetric software. We included 40 patients with adenocarcinoma and 11 patients with SCC, who underwent CT examinations more than once before surgical treatment. Tumor volumes and doubling times were obtained using three-dimensional volumetric computer software. Statistical analysis was performed using Mann-Whitney's U-test except for negative doubling times (doubling times less than 0 day). Negative doubling time was found in 5 of the 40 adenocarcinomas (13%), but not in any of the patients with SCC. Doubling time was beyond 400 days in 11 of the 40 adenocarcinomas (28%), but was always less than 400 days in SCC. The mean doubling time of SCC was 126+/-58 days (range, 39-221 days; median, 131 days), while that of adenocarcinomas, except for the negative doubling times, was 976+/-3134 days (range, 69-18,678 days; median, 258 days). Doubling time differed significantly between adenocarcinomas and SCC (p<0.01). In conclusion, the median doubling time of SCC lung cancers is less than that of adenocarcinomas, as measured with automated volumetric measurement software.