In the present work investigation demostrated the consumption and cost of oncologists drug in breast cancer in the service adults external consult of the Edgardo Rebagliati Martins National Hospital during september - december of 2007, for that used the methodology of the Paretos’s law, PDD/100 beds/day, applied to each oncologist drug in studies and finally calculate the cost that these occasions. The results based on the Pareto’s law demonstrated that paclitaxel was the oncologist drug that frecuently was used in september (41 %), october (37 %), november (40 %) and december (50 %), also paclitaxel was the outline of treatment that frecuently was used in september (30.98 %), october (30.81 %), november (33.88 %) and december (38.25 %). About consume the oncologist drug with major consume was paclitaxel with 19.28 PDD/100beds/day. Finally, demostrated that trastuzumab was the most e...