To evaluate the efficacy of imatinib in a practical setting, we registered 43 patients with newly diagnosed chronic myelogenous leukemia (CML) (group I) and 56 patients with previously diagnosed CML (group II) at 11 hematology centers in Nagasaki prefecture, Japan, from December 2001 to July 2005 and analyzed the molecular responses. Cytopenia, fluid retention, and skin rash were major adverse events, along with elevation in creatine phosphokinase levels. With a follow-up of approximately 3.5 years, imatinib treatment led to 88.7% overall survival (OS) and 85.2% progression-free survival (PFS) rates for group I, and 79.8% OS and 76.6% PFS rates for group II; the rates were not significantly different despite a lower average imatinib dose in group II. The rates of complete cytogenetic response at 30 months and major molecular response at 24 months were 86.1% and 62.5%, respectively, in group I, and 77.9% and 58.3% in group II; the rates were not significantly different. As has been reported by other groups, these results demonstrate that imatinib treatment can provide excellent clinical and molecular effects for not only newly diagnosed but also previously treated CML patients in practical settings that cover a wider variety of patients than clinical trials.