The equilibrium structure and two important molecular properties, the dipole moment and the nuclear quadrupole coupling constants, of diazirine have been investigated theoretically at high level of theory. Very accurate results, which can be favourably compared to the experiment, are presented. As far as the equilibrium structure is concerned, coupled-cluster approach with perturbative inclusion of triples and very large basis sets have been employed. Core correlation effects and basis set incompleteness have been taken into account in order to obtain best estimates of equilibrium geometry. The molecular dipole moment has been calculated at coupled-cluster level using bases of different quality including both diffuse and tight functions. Extrapolation to the infinite basis set limit has also been performed. In addition, the complete inertial nuclear quadrupole tensors, evaluated from the electric field gradients at nitrogen and hydrogen nuclei, have been computed at different level of theory: the multi-configuration self-consistent field, the Møller -Plesset many-body perturbation to second order and the coupled-cluster methods have been employed in conjunction with core-valence basis sets.