This study estimated lifetime cost of treatment for patients in the United Kingdom (UK) presenting with stage IV breast cancer. To determine patterns of treatment and resource use in the absence of direct observational data, a cancer physician panel was surveyed. The survey questionnaire described four predefined treatment phases: active treatment; follow-up after active treatment until disease progression; active supportive care after progression; and end-of-life care. Physicians were asked their major treatment strategies for each phase. Monthly cost and average lifetime cost per patient were calculated. Only five cancer registries in the UK document the proportion of breast cancer patients diagnosed with stage IV disease. Their data was used to estimate the incidence of metastatic breast cancer at presentation throughout the UK. This value, together with lifetime cost per patient and projected survival time, allowed approximation of the overall cost for this population of cancer patients in the UK. Annual incidence of stage IV breast cancer at presentation in the UK is approximately 2100; according to treatment practice in 2002, lifetime cost per patient is pound 12 500 and total population cost is approximately pound 26 million. The substantial economic burden associated with patients diagnosed with metastatic breast cancer should be considered when developing strategies for reducing its incidence such as increased awareness, screening and preventative measures.