Neutrino Mixing and the Pattern of Supersymmetry Breaking

We study the implications of a large $\nu_\mu - \nu_\tau$ mixing angle on lepton flavour violating radiative transitions in supersymmetric extensions of the standard model. The transition rates are calculated to leading order in $\epsilon$, the parameter which characterizes the flavour mixing. The uncertainty of the predicted rates is discussed in detail. For models with modular invariance the branching ratio $BR(\mu \to e \gamma)$ mostly exceeds the experimental upper limit. In models with radiatively induced flavour mixing the predicted range includes the upper limit, if the Yukawa couplings in the lepton sector are large, as favoured by Yukawa coupling unification.