Background. Many botanicals, particularly ornamental houseplants, contain crystals of calcium oxalate called raphides. Raphides have known toxic effects when chewed, including painful edema, vesicle formation, and dysphagia. We report a food-borne illness outbreak associated with ingestion of raphides. Methods. On February 24, 2003, the Chicago Department of Public Health was notified of multiple cases of oral burning and facial edema associated with lunch in an office cafeteria on February 21. The investigation included a case-control study, interviews with kitchen staff, an environmental inspection, and laboratory analysis of leftover foods. Results. Ten cases were identified, including one admitted to the Intensive Care Unit for potential airway obstruction secondary to severe edema, and another seen by Emergency Department staff for oral edema and pain. Ten of 10 case-patients reported oral stinging and burning, and 8 of 10 reported dysphagia. Four of 10 case-patients continued to have symptoms 2 weeks later. Food from the cafeteria's international buffet was consumed by 10 of 10 case-patients and by 1 of 22 control subjects (odds ratio = undefined); each of the 10 case-patients reported consumption of a Chinese vegetable entre from the international buffet and had no other foods in common. Plant material from the Chinese vegetable entre contained raphides. Conclusion. This outbreak was associated with consumption of raphides resembling those from common botanicals. Clinicians and public health practitioners should be aware of raphide-containing plants as a potential cause of food-borne illness.