This paper presents experiments which quantify the influence of the surface roughness on transient heat transfer from a substrate into liquid nitrogen. Using vapor-deposited metal films on glass substrates of different roughness the temperature variation of a surface subjected to a heat pulse was recorded. In addition optical methods were used to observe bubble formation and growth. Onset of nucleate boiling, temperature development and critical heal flux are investigated and compared with theoretical predictions. It is shown that for rough surfaces the onset of nucleate boiling occurs at lower temperatures and thus after smaller delay than for smooth surfaces. Furthermore, rough surfaces exhibit higher critical transient heat fluxes characterizing the transition to film boiling. The interpretation of photographs suggests that evaporation of liquid into one big vapor bubble dominates the transient heat transfer after onset of nucleate boiling.