Pentoxifylline is a xanthine derivative used in vascular disorders that is recognized as a safe drug for patients. The paper describes a rare case of fatal and suicidal pentoxifylline poisoning in an 82-year-old man with multiple preexisting diseases (arterial hypertension, coronary artery disease, type 2 diabetes, and intermittent claudication). The patient was admitted to the clinical toxicology unit approximately 2 h after the overdose and died 36 h after the admission despite intensive care. Multiple arterial blood gas analyses and other laboratory tests were performed during the hospitalization and are reported in the paper. Postmortem examination of the biological material was carried out with the use of histopathological techniques. The toxicological studies using chromatographic techniques coupled with mass spectrometry showed that postmortem blood levels of pentoxifylline have been found in the range which is described in the available literature to be toxic and lethal. The analysis of test results and clinical data showed that the patient died as a result of increasing circulatory and respiratory failure, complicated by disorders of the acid-base and electrolyte balance (respiratory alkalosis, concomitant lactic acidosis, and hypokalemia), hyperglycemia, and coagulation disorders.