A 40-year-old woman died shortly after complaining of non-specific symptoms after a pharmacist had accidentally given her the wrong medication. The woman's partner was not familiar with her medical history and the medical file had to be obtained from the family doctor. Autopsy findings and histological examination confirmed the clinically diagnosed autoimmune polyglandular syndrome without a tangible cause of death. Poisoning could not be demonstrated and no relation between the dosage error and death could be established. Laboratory tests revealed diabetic coma with ketoacidosis as the cause of death, which was probably caused by a prolonged lack of insulin administration. In addition to the clarification of legal issues, the complete post-mortem examination of orphan diseases is also relevant for achieving a better understanding of differential diagnostic aspects and complex pathophysiological contexts. Moreover, the genetic background often underlying such diseases should be a reason to inform the family of the deceased about the autopsy results. Only then can secondary preventive measures be taken in time.