In Mexico, breast cancer is the second most frequent cancer in oncology patients so high quality healthcare services and an efficient resource use is a priority. Currently, Mexican costs of different oncology treatments are general and incomplete. OBJECTIVES: To estimate in detail multiple breast cancer treatments costs in two oncology hospitals in the Mexican Institute of Social Security in Mexico City. METHODS: A case type model was constructed to identify resource use with the aid of expert opinion in radiotherapy, surgical, and chemotherapy services in two high speciality oncology hospitals (“Centro Médico Nacional La Raza” and “Centro Médico Nacional Siglo XXI”), during the last six-months of 2005. The total costs of each treatment was established with the case-mix technique and the research perspective was that of the health care payer's. Direct costs include: drugs, health staff wages, instrumental and medical equipment, laboratory and gabinet exams, and other resources for medical services. Indirect costs include: energy, water, gas, infraestructure, administrative costs, and others significant overheads. RESULTS: The costs estimation for surgery procedures were: Lumpectomy US$1075 and Mastectomy US$3291.80. In radiotherapy services tangential fields (TF) had a mean cost per intervention of US$849.90 and a breast complete cycle (BCC) was estimated in US$1284.10. Chemotherapy treatments showed different mean costs: CMF (6 cycles) US$624.90; FEC (4 cycles) US$1,682.50; FEC (6-8 cycles) US$2847.30; Navelbine (6 cycles) US$3,583.80, CarboGem (6 cycles) US$5374.70; Capacitabine (6 cycles) US$6,279.60; Epirubicina + Taxotere (4 cycles) US$11,607.30, and Trastuzumab US$16,572. CONCLUSIONS: Total costs of treatment per patient with breast cancer was estimated in Mexico (one surgical, radiotherapy and chemotherapy procedure was always included). The cheapeast treatment scenario included: lumpectomy, TF and CMF with a cost of US$2264.20 and the highest cost scenario was found using rebuilding surgery, BCC and Trastuzumab with a cost of US$20,477.10.