To assess α+-thalassemia deletion alleles, β-thalassemia mutations and haplotypes linked to the HBB*S cluster in a sample of 130 unrelated sickle cell anemia (SCA) patients (55% female) from Belém, Pará State, for their possible effects on the patients' survival. -α3.7, -α42, -α20.5, and –MED α+-thalassemia deletion alleles were investigated using multiplex gap-PCR method. Characterization of β-thalassemia mutations was made by direct genomic sequencing of the β-globin gene amplified through polymerase chain reaction (PCR). Haplotypes were determined by analysis of six polymorphic restriction sites [(1) XmnI-5′γG, (2) HindIII-γG, (3) HindIII-γA, (4) HincII-ψβ, (5) HincII-3′ψβ, and (6) HinfI-5′β] followed by restriction digestion and agarose gel electrophoresis. Twenty-one patients (16%) presented -α3.7 thalassemia. Sixteen of those (76%) were heterozygous (-α3.7/αα) and 5 (24%) were homozygous (-α3.7/-α3.7). -α4.2, -α20.5 and –MED deletions were not found. Nine cases of sickle cell-β thalassemia were found and four different β-thal mutations were identified: β+ −88 (C>T), 3.8%; β+ codon 24 (T > A), 1.5%; β+ IVSI-110 (G > A), 0.7% and β (IVSI-1 (G > A), 0.7%. No differences according to age were observed in -α3.7 deletion, β-thalassemia and HHB*S haplotypes distribution. Our results suggest that although α- and β-thalassemia and βS haplotypes may have modulating effect on clinical expression and hematological parameters of SCA, these genetic variables probably have little influence on the subjects' survival. Am. J. Hum. Biol. 22:573–577, 2010. © 2010 Wiley-Liss, Inc.