Materials used for dental impressions are usually safe. This study describes a case of fatal anaphylaxis that appeared immediately after the oral mucosa came into contact with an alginate paste used for dental impressions. The cadaveric examination and the postmortem toxicology report confirmed that the cause of death was anaphylactic shock. The patient was affected by both cardiovascular and lung diseases that worsened the condition and forbade the use of epinephrine. To the authors' knowledge, dental impression materials, and alginate in particular, have not been reported previously as being a cause of anaphylaxis.