S100B is a small calcium-binding protein expressed primarily by astrocytes involved in several pathologies. Several studies have shown S100B protein immunoreactivity (S100B-IR) in brain specific areas, and some of them showed the cells identity under physiological and/or pathological conditions. This review reports the S100B-IR distribution in the brain specific areas of different adult mammals and complement with our results in order to provide a complete overview about the S100B-IR distribution and cell identity. This review highlights a heterogeneous distribution of S100B-IR in prosencephalic, diencephalic, brainstem and cerebellum areas. Regarding cellular identity, the co-localization of S100B-IR and GFAP-IR occurred predominantly in periventricular areas, in the hippocampus and the septal area in contrast with cortical regions. In addition, cells S100B-IR but not GFAP-IR were also found in these areas. The analysis throughout the rostro-caudal axis of the brain showed that S100B-IR did not present colocalization with neurons (NeuN-IR). This complete description can be potentially used for researches that aim to consider changes in S100B expression in different pathologies.