Measurements of the nucleon structure function FN from deep inelastic muon scattering on deuterium are presented. The neutron structure function is deduced from a comparison with hydrogen data. In addition the charge and the momentum distributions of the u and d valence quarks in the nucleon are extracted together with an estimate of the momentum distribution of the sea quarks. A comparison of the nucleon structure functions in deuterium and iron shows that the quark distributions in the quasi-free nucleons of deuterium are different from those for bound nucleons in iron.