The definition of the methods for localizing the booster field used in the conservative treatment of early breast cancer is often blurred in several studies in the current literature. This paper is aimed at reporting a surgical-radiological method more objective than the clinico-anamnestic one used, so far, for planning the booster field. To this purpose 33 patients underwent conservative surgery in healthy tissue and radiopaque clips were inserted at the margins of the excision cavity. The booster field as defined with clinico-anamnestic standards was then simulated and later verified by a radiation therapy simulator. The clinical fields thus set up were correct in 15/33 cases. The authors discuss their results and compare them with literature data. The importance of the use of the surgical-radiological method to localize the booster field is stressed.