An interpretation of the pitch and time dependence of diffusion in the cholesteric liquid crystalline phase is proposed. Experimental results on nematics twisted by chiral dopands are discussed. The model predicts a decay of the translational diffusion coefficientDpin the helix direction with the observation time and a decrease ofDpwith shorter pitch lengthPo, in accord with experiment. From comparison with experimental data it is concluded that rotational diffusion in these samples is a collective phenomenon.