-Medulloblastoma (MB) is the most common malignant brain tumor in childhood. The alterations found include: presence of oncoproteins p53 and HER2, elevated mitotic index, and presence of neuronal differentiation. The aim of this study was to determine the immunohistochemical expression of markers Ki-67, NeuN, synaptophysin, HER2 and p53 in 40 MB samples and their correlation with clinicopathologic parameters and survival. In 29 patients (72.5%), ≥20% of cells were positive for Ki-67. Males showed greater ki-67 expression (p=0.02) and smaller survival rates (p=0.002). NeuN and synaptophysin were negative in 16 (40%) and 8 (20%) cases, respectively. P53 was positive in 18 (45%) cases, with 11 (61%) weakly positive and 7 (39%) strongly positive. HER2 was positive in 23 (57.5%) of the samples and did not show statistical association with survival (p=0.07).KEy woRds: medulloblastoma, immunohistochemistry, Ki-67, NeuN, synaptophysin, HER2, p53, survival analysis. expressão imunoistoquímica dos marcadores ki-67, neun, sinaptofisina, p53 e her2 em meduloblastoma e sua correlação com os parâmetros clínico-patológicosResumo -Meduloblastoma (MB) é o tumor maligno encefálico mais freqüente na infância. dentre as alterações encontradas estão: a presença das oncoproteínas p53 e HER2, elevado índice mitótico e presença de diferenciação neuronal. o objetivo deste estudo foi determinar a expressão imunoistoquímica (IMQ) dos marcadores Ki-67, NeuN, sinaptofisina, HER2 e p53 em 40 amostras de MB, correlacionando-as com parâmetros clinicopatológicos e com a sobrevida. Vinte e nove pacientes (72,5%) apresentaram 20% ou mais das células positivas para Ki-67. os pacientes do sexo masculino apresentaram maior expressão do Ki-67 (p=0,02) e também menor sobrevida (p=0,002). NeuN e sinaptofisina foram negativos em 16 (40%) e 8 (20%) casos, respectivamente. P53 foi positivo em 18 (45%) casos, sendo 11 (61%) fracamente positivos e 7 (39%) fortemente positivos. HER2 foi positivo em 23 (57,5%) das amostras e não demonstrou associação estatística com a sobrevida (p=0.07).PAlAVRAs-cHAVE: meduloblastoma, imunoistoquímica, Ki-67, NeuN, sinaptofisina, HER2, p53, sobrevida. Medulloblastoma (MB) is the most common malignant brain tumor in children, accounting for about 20% of all primary tumors of the central nervous system (cNs), with a peak of incidence at 5-7 years-old. These tumors have an aggressive behavior and despite treatment, the 5-year survival rate is 60% 1,2 . For therapeutic and prognostic purposes, patients are divided in groups of high and low risk, according to the staging proposed by chang et al. (1969) 3 , age at the time of diagnosis, and presence of residual tumor 4,5 . A more accurate assessment of risk in children with MB can be done using a combination of clinical, histopathologic, and molecular prognostic factors 4,6,7 .