Although Fischer's convention for stereoisomers is useful for simple molecules, the stereochemistry of complex biochemical molecules is often poorly indicated in textbooks. This article reports on errors in stereochemistry of complex hydrosoluble vitamin B12 molecule. Twenty-five popular biochemistry textbooks were examined for their treatment of the stereoisomery of vitamin B12. Mistakes, discrepancies, and oddities reported in vitamin B12 are just an example of this problem. Biochemistry textbook authors and teachers should pay more attention to the stereoisomery of biochemical molecules to avoid students' confusion.