The features of electron density in the complexes of substituted pyridines have been studied with a special attention to the N ... I halogen bonding. The source function indicates that the major contribution to the electron density at the bond critical point of N ... I interaction goes from the basin of iodine atom. The delocalization indices for halogen bond N ... I quantitatively correlate with the sum of atomic sources of iodine and nitrogen. This finding allows estimating the delocalization indices directly from the electron density. The delocalization indices of halogen bond are well correlated with the basicity pK(BI2) according to the diiodine basicity scale. (C) 2014 Elsevier B.V. All rights reserved.