OBJECTIVE: To establish the frequencies of HLA-A, B, DRB1 and DQB1 specificities in a racially admixed sample of the city of Teresina, Piauí to characterize its genetic composition. METHODS: Polymerase chain reaction-sequence specific primers (PCR-SSP) were used to determine HLA-A, B, DRB1 and DQB1 specificities of 97 unrelated healthy racially admixed people of Teresina. The genotypic frequencies were estimated and compared to those described in samples of Brazilian Caucasian, Portuguese, Black and Amerindian populations using Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA). RESULTS: The frequencies of HLA-A, B, DRB1 and DQB1 specificities observed in the study sample were intermediate between Blacks and Caucasians and the typical elevation of HLA-specificities seen in the Amerindian race was not observed in the study population. The PCA and HCA analysis revealed that Teresina's racially admixed are very close to both Black and Caucasian and do not show similarities with the Amerindians. CONCLUSION: The genetic composition of Teresina's racially admixed is predominantly bi-hybrid of genes originated from Blacks and Caucasians with little contribution from Amerindian genes.