DFT/B3-LYP(6-31++G**) calculations are used to provide information on closed N-H . . .O H-bonded complexes, containing two hydrogen bonds. The studied model systems with two ii-bonds are the 2-pyridone dimer, 2-pyridone-H2O and 2-pyridone-CH3OH. For the sake of comparison, the open, singly H-bonded complex 2-pyridone-CH3OCH3 is also examined. In the dosed H-bonded complexes, an II-bond cooperativity effect has been observed, but it depends on the linearity of the hydrogen bond N-H . . .O. For the 2-pyridone dimer, which has the perfect, linear geometry, the strongest cooperativity is observed, whereas in all the other closed Ii-bonded systems, the cooperativity is reduced by deformation from the linear H-bond geometry. These observations are illustrated by different correlations established between the II-bond angle and other characteristic II-bond parameters.