Letus present a unique clinical case course of autoimmune non paraneoplastic myasthenic syndrome of Lambert–Eaton on the background of pregnancy, in the 24 years old patient, with a 3-year history of the disease. Throughout the pregnancy, birth and early postpartum period, patient was taking a stable unmodified drug therapy, which allowed observing "natural" course for neuromuscular disease. The first trimester of pregnancy proceeded without deterioration of the myasthenic syndrome. From the middle of the second trimester (19–20 weeks gestation), and the entire third trimester until parturition, the patient's condition for neuromuscular disease has improved, which was accompanied by an increase in strength of proximal limb muscles and the positive dynamics of the basic parameters of neuromuscular transmission. Deliveries came on ime, preceeded safely through vaginal delivery, without weakness of generic forces. There was born clinically healthy male child, weighing 2970 g, growth of 52 cm (7/8 Apgar score). However , on the second day in the newborn was marked negative dynamics of muscular hypotonia, extinction of neonatal reflexes, sucking weakness, episodes of apnea, which required tube feeding and non invasive oxygen support. Neuromuscular defect was transient in character and resolved within 5–7 days with administration in the morning hours of 20 mg of prednisone parenteral. The child was discharged with full recovery of function of the neuromuscular system on the 13th day breastfed. Shortly after birth the mother appeared in a state of negative dynamics: the increased weakness of the proximal muscles of the legs and arms, deteriorated parameters of the neuromuscular conduct. By analogy with myasthenia there appeared the similar influence of pregnancy on the Lambert Eaton myasthenic syndrome: 1) improvmem of the neuromuscular disease in II–III trimester of pregnancy, 2) intact ability to birth vaginally, 3) no evidence of neuromuscular disease in newborn at birth, 4) one day delay in the development of transient neonatal myasthenic syndrome, 5) postpartum mothers deterioration that increases while breastfeeding