The enzyme erythronate-4-phosphate dehydrogenase, encoded by the pdxB gene, catalyses the conversion of erythronate-4-phosphate to 3-hydroxy-4-phospho-hydroxy-α-ketobutyrate. It belongs to the d-isomer-specific 2-hydroxyacid dehydrogenase family. It is essential for de novo biosynthesis of vitamin B6 (pyridoxine). Crystal structure of erythronate-4-phosphate dehydrogenase from Salmonella typhimurium LT2 has eight protein molecules in the asymmetric part of the unit cell. Each protein molecule consists of three structural domains: the lid domain, the nucleotide-binding domain, and the C-terminal domain. The latter domain has a unique fold and is largely responsible for dimerization. Interestingly, in all protein molecules of the enzyme the C-terminal domain displays significantly different conformations. The NAD was found in the active site bound to the nucleotide-binding domain. Our structural data allow a detailed understanding of cofactor recognition site, and provide insights into PdxB catalysis.