β-Thalassemia (β-thal) is a hereditary disease with at least 200 known causative molecular defects, with a limited number of distinct mutations predominating in any given population. The Brazilian population is one of the most heterogeneous in the world. Although occurrences of β-thal in this country have been recognized for a long time and previous studies have shown important regional differences related to the mutational profile, no extensive analysis of mutations of the HBB gene has been carried out in Brazil. We examined 1011 teenagers from Bahia, a state located in the northeast of Brazil. Hematological data were obtained using automated cell counting, hemoglobin (Hb) profiles were studied by high performance liquid chromatography (HPLC), and DNA was analyzed by automated sequencing. None of the four Mediterranean mutations that are most frequently found in South and Southeast Brazil (HBB: c.118C>T; HBB: c.93-21G>A; HBB: c.92+1G>A; HBB: c.92+6T>C), was found to be responsible for thalassemia in the cases that we studied. One heterozygote for a frameshift mutation at codon 44 (-C) was identified. This is the first study to determine the prevalence and profile of β-thal in Bahia State. For the first time in Brazil, we report the occurrence of the HBB: c.135delC mutation in the β-globin gene.