This aims of this work were to document the natural history of nerve injuries and their repair under controlled conditions in order to ascertain the outcome of different types of nerve injury and to compare the outcome of the same injuries in motor nerves and mixed nerves. The sheep model was selected as its peripheral nerves as a similar size, and behave in a similar manner to, human peripheral nerves. A set of six standardised nerve injuries (normal control, neurapraxia, axonotmesis, neurotmesis and suture repair, neurotmesis and entubulation, and nerve graft) was created in both the facial (motor) nerve and the median (mixed) nerve. The function of the nerves and their target muscles was assessed using nerve conduction studies (maximum conduction velocity, distribution of conduction velocities, refractory period), single-fibre electromyography (jitter), target muscle tension and mass, and nerve fibre morphometry. In the carefully controlled conditions of the experiments, for both nerves the transection injuries had a poorer outcome than the non-transection injuries. This effect was more marked in the median nerve than in the facial nerve suggesting that the type of nerve affected the outcome of injury. Maximum conduction velocity and jitter were determined to be the most useful tests for use in the clinical management of nerve injuries. Distribution of conduction velocities, a nerve conduction test based on collision theory, may be too sensitive to be of use in the management of mechanical nerve injury but may have a valuable role in the assessment of more subtle conditions such as neuropathies and Bell’s palsy. Nerve fibre morphometry discriminated between the different injuries and remains a useful tool in a research setting.