This study aims to present a case of acute mercuric chloride poisoning at a potentially lethal dose treated with the antidote – 2,3-dimercapto- 1-propanesulfonic acid (DMPS) and continuous renal replacement therapy (CRRT) combined with CytoSorb. A 21-year-old woman was admitted to a hospital with abdominal pain, vomiting, and suspected gastrointestinal bleeding after taking 5000 mg of mercuric chloride for suicidal purposes. Due to the patient deteriorating general condition and multiple organ damage, on the third day she was transported to the Clinic of Anaesthesiology and Intensive Care (CAaIC), Łódź, Poland. Laboratory tests confirmed features of acute kidney injury and high mercury levels in the blood (1051 μg/l) and urine (22 960 μg/l) – DMPS therapy and CRRT combined with CytoSorb were instituted. Due to nervous system complaints (headache, dizziness), a lumbosacral puncture was performed – the mercury concentration in the cerebrospinal fluid (CSF) was 5.45 μg/l. During a colonoscopy, significant diagnostic abnormalities revealed features of colonic mucosal necrosis. The treatment resulted in a decrease in subjective complaints, decreased mercury levels in biological material, and improved parenchymal organ function. On the 15th day of therapy, the patient was transferred to the primary care center for further treatment. The case confirms the possibility of improvement of patient condition following ingestion of a potentially lethal dose (5 g) as a result of the initiation of appropriate therapy even on the third day. The presence of mercury in CSF confirms that inorganic mercury compounds (mercuric chloride) can pass through the blood-brain barrier after oral ingestion. Int J Occup Med Environ Health. 2023;36(5):685–92