This book constitutes the refereed proceedings of the Third Brazilian Symposium on Bioinformatics, BSB 2008, held in Sao Paulo, Brazil, in August 2008 - co-located with IWGD 2008, the International Workshop on Genomic Databases. The 14 revised full papers and 5 extended abstracts were carefully reviewed and selected from 41 submissions. The papers address a broad range of current topics in computational biology and bioinformatics featuring original research in computer science, mathematics and statistics as well as in molecular biology, biochemistry, genetics, medicine, microbiology and other life sciences.