  Nucleon form factors are calculated in a relativistic diquark--quark picture
based on the Nambu--Jona-Lasinio model. The nucleon wave function is obtained
in a static approximation to the quark exchange interaction between the valence
quark and the diquark. We evaluate the valence quark and $0^+$--diquark
contribution to the nucleon electromagnetic and weak currents. We find
reasonable electric charge radii, magnetic moments as in the additive diquark
model, and $g_A \approx 1$. We discuss the dependence on the model parameters.
