Increasing the number of breast cancer patients in follow-up involves increased costs and, with limited health care resources, there is a need to evaluate the cost-benefit to the patient of follow-up regimens. We present a randomized prospective study to evaluate the cost-benefit of intensive follow-up in the early detection of relapses in patients with breast cancer. One hundred and twenty-one patients were randomized to standard clinical follow-up (n=63) or to an intensive follow-up (n=58) that included diagnostic laboratory tests and imaging designed to detect early relapse following curative treatment. All patients had annual mammography. The number of scheduled outpatient appointments kept were 359 in the standard clinical follow-up and 355 in the intensive follow-up group. After a median of 3 years of follow-up, there were 28 relapses, 11 in standard clinical follow-up, and 13 in the intensive follow-up group. The overall cost of follow-up was 24,567 euros in the standard clinical follow-up group and 74,171 euros in the intensive follow-up group. Performing complimentary investigations in breast cancer follow-up is associated with higher costs without difference in early detection of relapses.