Disseminated cells from primary solid tumors are considered to be the cause of metastases formation and relapse of disease. Consequently, their detection is of high importance for staging, prognosis and decisions about adjuvant therapy. Residual disease is conventionally detected by histological evaluation of biopsy specimens. Continuing efforts to increase the sensitivity to identify occult tumor cells in lymph node, bone marrow and blood have led to the development of various strategies. This review will discuss histological, immunological and molecular approaches to detect micrometastases from solid tumors.