We present a clear evidence for N2O 4.5 ¿m non-local thermodynamic equilibrium (non-LTE) emissions in the daylight stratosphere and mesosphere from measurements by the MIPAS experiment on board Envisat. We have used non-LTE radiative transfer models in order to quantify the magnitude and extent of the non-LTE deviation of N2O(001) in the Earth's atmosphere. The departure from LTE in N2O during daytime commences at altitudes around 40--50 km, but have significant effects (10%) on daytime limb radiance down to tangent heights of 20 km. The enhancement increases rapidly with altitude, being 20--80% at 50 km, and reaching factors of 2--8 in the lower mesosphere. This study shows that the enhancement is mainly produced by absorption of solar radiation by N2O at 4.5 ¿m and by V-V collisions with N2(1). Non-LTE effects are also significant at nighttime, where LTE calculations overpredict N2O radiances by 10--20% at 40--55 km tangent heights.