Cyanide has seen widespread use as the toxic agent in many product tampering cases and is potentially the most lethal of all agents used. The ingestion of cyanide through tampered food, drink, or drugs has resulted in the death of at least 14 people over the past decade. Prominent tampering incidents and their common features are reviewed. Prominent cyanide tampering incidents are discussed, and the importance of requesting appropriate toxicological tests is emphasized. Potential tampering motives are examined, including terrorism, sabotage, homicide, insurance fraud, malicious mischief, and attention-seeking. Limitations of tamper-evident packaging are noted. 61 references