High level ab initio calculations find that nitrenes are more stable than carbenes, as indicated by the computed enthalpy differences of 25-26 kcal/mol between triplet phenylnitrene and the isomeric tripler pyridylcarbenes. More generally, the greater thermodynamic stability of nitrenes manifests itself in the finding that the N-H bond dissociation energies (BDEs) of aminyl radicals are approximately 20 kcal/mol lower than the C-H BDEs of analogous alkyl radicals. The greater thermodynamic stability of nitrenes, relative to carbenes, is attributed to the large amount of 2s character in the orbital that is occupied by the lone pair of electrons in nitrenes.