The follow-up of colon cancer patients by monitoring serum carcinoembryonic antigen has advantages (better survival after early detection of recurrence by CEA rise) as well as disadvantages (false-positive rise of CEA, and early detection of incurable recurrences in asymptomatic patients). The effects of CEA follow-up on quality-adjusted life expectancy (QUALE) of patients with curatively resected colon carcinoma have been simulated by a Markov analysis using literature data. The value of CEA seems insignificant and varies, depending on the literature data used, from a mean increase of QUALE by 6 days (+0.4%) to a mean decrease by 2 days (-0.07%). This value depends on patient-related variables; the negative effects of CEA especially predominate in older patients with favourable Dukes' stages of primary tumour.