Seeds of the castor bean plant Ricinuscommunis L (CB) contain ricin toxin (RT), one of the most poisonous naturally-occurring substances known. Ricin toxin, a water-soluble glycoprotein that does not partition into the oil extract, is a ribosome-inactivating toxin composed of two chains, labeled A and B. Severity of the toxicity varies depending on the route of exposure to the toxin. Inhalational is the most toxic route, followed by oral ingestion. Orally-ingested RT accumulates in the liver and spleen but other cells are also affected. The main clinical manifestations are also related to the administration route. Oral ingestion of CB or RT results in abdominal pain, vomiting, diarrhea, and various types of gastrointestinal bleeding that leading to volume depletion, hypovolemic shock, and renal failure. Inhalation of the toxin presents with non-cardiogenic pulmonary edema, diffuse necrotizing pneumonia, interstitial and alveolar inflammation, and edema. Local injection of RT induces indurations at the injection site, swelling of regional lymph nodes, hypotension, and death. An enzyme-linked immunosorbent assay (ELISA) has been developed to detect RT in animal tissues and fluids. Ricinine, an alkaloid of CB, can be detected in rat urine within 48 h of RT exposure. Supportive care is the basic treatment and standard biowarfare decontamination protocols are used for RT intoxication. Dexamethasone and difluoromethylornithine might be effective treatments. This review examines the clinical and molecular aspects of ricin toxicity.