The clinical significance of micrometastasis in patients with colorectal cancer has been investigated by immunohistochemical and molecular biological methods for several decades. However, no general consensus of the clinical significance of micrometastasis has been established. The presence of isolated tumor cells and occult micrometastases in lymph nodes may be an important information to determine the candidate for adjuvant chemotherapy among patients with colorectal cancer without overt lymph node metastasis. The research of circulating tumor cells and disseminated tumor cells would be expected to elucidate the mechanism of chemo-resistance and apply developing new anti-cancer agents. The detection of micrometastasis may contribute to create "tailor-maid treatment" for patients with colorectal cancer.