In this study, the stability of clusters formed by the trans- and cis-isomers of nitrous acid (HONO) with dimethylamine (DMA) and water has been characterized by density functional theory. The large red shifts of the OH-stretching transitions of both HONO isomers in the clusters indicate the formation of strong hydrogen bonds. At standard temperature and pressure, H₂O (acceptor) binds to HONO (donor) with binding energies of −25.0 to −24.6 kJ mol⁻¹, less stable than those of DMA (acceptor) with HONO (donor) (−50.5 to −45.3 kJ mol⁻¹). Our findings indicate that hydration enhances proton transfer from HONO to DMA, and consequently increases the interaction strength (binding energies = −67.8 to −78.6 kJ mol⁻¹). The topological and generalized Kohn–Sham energy decomposition confirms strong hydrogen bond interactions. The clustering of HONO with DMA in the atmosphere is negligible as compared to the important H₂SO₄–DMA clusters.