Malignant phyllodes tumor (MPT) is a rare breast malignancy. Because of the scarcity of the disease, there are no evidence-based treatment or follow-up guidelines established. This study evaluated the survival of MPT patients to create recommendations for management. We identified 752 cases of malignant phyllodes tumors in the California Cancer Registry from the years 1988 to 2003. Relative survival was determined using Berkson-Gage life table analysis which was then compared with the relative survival of nonphyllodes breast cancer patients. For MPT patients, the relative annual survival at 1 year was 94 per cent and at 10 years was 99.6 per cent. Thus, after 10 years, these patients are no more likely to die than the general population. At 10 years, the relative cumulative survival of the MPT patients was 87.4 per cent, whereas the nonphyllodes breast cancer patients had only a 57.2 per cent relative cumulative survival. MPT patients with localized disease had a higher 10-year relative cumulative survival than those with regional disease (90.9% vs. 61.5%, P < 0.001). MPT has a good prognosis, particularly in patients with localized disease. After 10 years, MPT patients have no increased mortality relative to the general population. Clinicians should plan these patients' follow-up accordingly.