  We calculate the rates for the charged lepton flavour violating (LFV) decays
l_i -> l_j gamma, tau -> l pi, tau -> l eta('), mu^- -> e^-e^+e^-, the six
three-body leptonic decays tau^- -> l_i^- l_j^+ l_k^- and the rate for mu-e
conversion in nuclei in the Standard Model (SM3) extended by a fourth
generation of quarks and leptons (SM4), assuming that neutrinos are Dirac
particles. We also calculate branching ratios for K_L -> mu e, K_L -> pi^0 mu
e, B_{d,s} -> mu e, B_{d,s} -> tau e and B_{d,s} -> tau mu. We find that the
pattern of the LFV branching ratios in the SM4 differs significantly from the
one encountered in the MSSM, allowing to distinguish these two models with the
help of LFV processes in a transparent manner. Also differences with respect to
the Littlest Higgs model with T-parity are found. Most importantly the
branching ratios for l_i -> l_j gamma, tau -> l pi, tau -> l eta('), mu^- ->
e^-e^+e^-, tau^- -> e^-e^+e^-, tau^- -> mu^- mu^+ mu^-, tau^- -> e^- mu^+ mu^-
and tau^- -> mu^- e^+ e^- can all still be as large as the present experimental
upper bounds but not necessarily simultaneously. Also the rate for mu-e
conversion in nuclei can reach the corresponding upper bound.
