Increasing evidence supports the function of p53 as suppressor gene. Auto-antibodies against the product of this gene are frequently found in cancer patients. There is little information on the stages of the diseases where these antibodies are detected and on their clinical relevance. To address these questions we investigated antibodies (immunofluorescence and immunoprecipitation) against wild type and mutant type p53 in sera from patients with metastatic breast cancer and correlated the results with characteristics of patients’ subgroups and the clinical course of the disease. The study included 50 patients, half of them with detectable antibodies against p53. There was no coincidence of antibodies against p53 wild type and mutant type. Antibodies against p53 were found more frequently in low-risk (good prognosis) than in high-risk (poor prognosis) patients. The intervals from diagnosis to death but not from diagnosis to test were longer in antibody-positive than in antibody-negative patients. The results suggest that antibodies against p53 are more frequently detected in a subclass of patients with favorable than in one with poor prognosis of metastatic breast cancer.