The reactions of the positive ions in N2 O have been studied mass spectrometrically at pressures up to approximately 2 Torr and at temperatures in the vicinity of 300°K, that is, under conditions similar to those which prevail in a gas phase radiolysis experiment. The ${\rm N}_{2}{\rm O}^{+}$ parent ion associates with a N2 O molecule to form a $({\rm N}_{2}{\rm O})_{2}{}^{+}$ dimer, with a termolecular rate constant of $4.8\pm 0.5\times 10^{-28}\ {\rm cm}^{6}/\text{molecule}^{2}\text{-}{\rm sec}$ at 300°K. The ratio $({\rm N}_{2}{\rm O})_{2}{}^{+}/{\rm N}_{2}{\rm O}^{+}$ shows a sharp decrease with an increase in temperature. The NO+ fragment ion also associates with a N2 O molecule to form the ${\rm NO}^{+}\cdot {\rm N}_{2}{\rm O}$ association ion. At pressures greater than 1 Torr, this ion associates with a second molecule of N2 O to form ${\rm NO}^{+}\cdot ({\rm N}_{2}{\rm O})_{2}$