Objective: The aim of this retrospective study was to evaluate the prognostic significance of lymphopenia associated with chemotherapy in patients with colorectal cancer who received adjuvant chemotherapy after undergoing potentially curative surgery. Summary of background data: Lymphocyte plays an important role in anti-tumor immunity. Lymphopenia is sometimes induced during the period of adjuvant chemotherapy after potentially curative surgery for colorectal cancer. However, the prognostic significance of lymphopenia associated with chemotherapy is unknown. Methods: One hundred and fifteen patients who received adjuvant chemotherapy after potentially curative surgery for stage II/III colorectal cancer were enrolled in this study. All patients were classified into two groups, the lymphopenia group and the normal group, according to minimum lymphocyte count during the period of adjuvant chemotherapy. Lymphopenia was defined as a lymphocyte count of less than 1,000/ÃÂ¼l. Lymphopenia associated with chemotherapy was found in 17 of the 115 patients (14.8%). Results: Lymphopenia was associated with a worse disease-free survival (p=0.018). Moreover, in a multivariate analysis, lymphopenia associated with chemotherapy was identified to be an independent prognostic factor.