Phenprocoumon is a derivative of coumarin, used as a preventative anticoagulant and in the treatment of thromboembolisms. On account of its pharmacodynamic and pharmacokinetic properties, strict surveillance of the patient is necessary. We report on two cases of undocumented administration of this active pharmaceutical ingredient. A 57-year-old woman was discovered by her husband in an inanimate state. The post-mortem examination revealed many extensive haematomas. On account of a suspicion of third-party negligence, an autopsy was performed the same day, during which was established that the cause of death was a clotting abnormality, the cause of which remained unclear. Toxicological analyses revealed a concentration of phenprocoumon of 7.8 mg/l. A 76-year-old man admitted himself to hospital immediately upon returning from a stay abroad. In hospital, extensive haematomas and a massive clotting abnormality (prothrombin ratio<10%) were discovered. A blood sample taken the following day yielded evidence of a phenprocoumon concentration of 3.1 mg/l. According to his general practitioner, no corresponding medications had been prescribed. Suspicion of foul play in the introduction of this active agent resulted in a police investigation. Both cases demonstrate the necessity of toxicological analyses in cases of clotting abnormalities.