Both central and peripheral nervous system damage is rather frequent in systemic connective tissue diseases. CNS damage is mainly due to changes in vessel walls, resulting in ischaemic foci in the brain. Peripheral neuron damage is the cause of neuropathies, usually of axonal or axonal--demyelinating type: mononeuropathy, multifocal mononeuropathy and polyneuropathy. The neuropathies may be caused also by changes in vascular walls, including these in nerve-nutrient vessels. Electroneurography is the main diagnostic method in this group of disorders. It permits to assess whether a given nerve is damaged, whether the damage is local or generalised, whether motor and sensory fibers are equally affected. Besides, the pathological process intensity and dynamics may be evaluated, as well as the character of the lesion (axonal or demyelinating). Electromyography is a complementary technique in the diagnosis of, but the main diagnostic method in primarily myogenic pathology (such as e.g. polymyositis, dermatomyositis, scleromyositis, the Sharp syndrome, etc.), frequently present in the course of collagenoses. Electromyography allows to differentiate between the primarily myogenic and neurogenic muscle changes. On finding primarily myogenic changes in EMG recording, not only the lesion intensity can be evaluated, but sometimes also its dynamics, i.e. whether it is of acute or chronic character. Electroneurography and electromyography may be also helpful in the prognosis and in treatment monitoring.