Acute poisoning in children is one of the most frequent reasons for seeking medical care and hospitalization in intensive care units, but it is extremely rare in children of the first year of life. On the example of the clinical case, the peculiarities of the course of acute severe methadone poisoning in a two-month-old child against the background of natural feeding are considered. The main data of history and clinical-laboratory examination are reflected, which allowed to suspect acute poisoning in a timely manner and to carry out reasonable intensive therapy, against the background of which the maximum rapid improvement of the child s condition is achieved. The algorithm of differential diagnosis of comatose state in children is presented, which can be used in all cases of sudden suppression of consciousness of unclear genesis. Special attention is paid to the need for maximum early recognition of exogenous poisoning and targeted pathogenetic treatment aimed at elimination of toxicant metabolites. A distinctive feature of this case was the severe course of acute methadone poisoning in the infant with the development of coma and respiratory distress, which regressed against the background of the treatment carried out with the full recovery of the patient.