Capecitabine is an oral prodrug to 5-fluorouracil (5-FU). The primary target of 5-FU is thymidylate synthase (TS). A mainstay of colorectal adenocarcinoma chemotherapy is inhibition of TS, which may be one of many determinant factors when predicting the outcome of chemotherapies based on fluoropyrimidine treatment. This retrospective study included 39 patients with advanced colorectal adenocarcinoma treated with capecitabine. Response was assessed by measuring the amount of tumour in the course of treatment. TS expression was evaluated by scoring the immunohistochemical (IHC) reaction and assessing the predominant IHC reaction pattern. This study showed significant correlation between the predominant IHC reaction pattern and response, but no correlation between IHC score and response. The predominant IHC reaction pattern may be a useful parameter in prediction of clinical outcome in patients treated with capecitabine.