After more than a decade of ambiguity, polycarbodiimides have been discovered to be fully regioregular when containing two sterically inequivalent pendant groups. To directly probe the regioregularity, a series of nitrogen-15 isotopically enriched polycarbodiimides with various combinations of pendant groups was synthesized using a variety of catalysts. Subsequent N-15 NMR analysis was performed on each of the labeled polymers to accurately determine the preferred regioisomer(s) and any particular bias present for monomer insertion. More sterically hindered substituents, i.e., aromatics, were found to be relegated to the imine nitrogen while the less hindered aliphatic groups were, in all cases, located on the amine nitrogen. No electronic biases were observed and the use of different titanium(IV) catalysts yielded the same regioisomer. Carbodiimides bearing sterically equivalent groups were polymerized to form regioirregular polymers with a 1:1 mixture of both regioisomers.