This document proposes a method for segmenting breast tumors in ultrasound images based on neutrosophic similarity score and level set (NSSLS). An ultrasound image is represented in the neutrosophic set domain and a neutrosophic similarity score is defined to measure the belongingness to the true tumor. A level set method is then used to segment the tumor from the background using the similarity score values. The proposed method maps pixels into the neutrosophic set domain based on intensity and gradient values to define membership values. Additional criteria like local mean intensity and local homogeneity are also used. The similarity score is calculated between pixels and an ideal object to identify the degree of belongingness under different conditions. Finally, the level