The stability of vapor-deposited amorphous molecular films is investigated by integral and angular-resolved laser scattering and by scanning electron microscopy. The processes of nucleation and crystal growth are followed by time-resolved speckle interference patterns and also by fluorescence intensity measurements. The crystallisation kinetics is of first order with time constants between hours and years, depending mainly on the chain lengths of the film constituting molecules. The diffusion coefficients of the latter are determined on silica substrates and are correlated with the crystallisation kinetics of the films.