OBJECTIVE: To characterize reports to poison centers involving liquid medication errors associated with the use of dispensing cups. design: Case series reported by 16 US poison centers over an eight-day period. SETTING: Calls to poison control centers, predominantly but not exclusively from homes. PATIENTS: Children and adults. RESULTS: Of 34 reported cases, most (79 percent) involved a two- to threefold dosing error, and most (94 percent) involved an error in a single dose of medication. Cough and cold preparations were implicated in 65 percent; acetaminophen elixirs in 18 percent. Three major causes of dosing errors were identified, including teaspoon/tablespoon confusion, assumption that the dispensing cup was the unit of measure, and assumption that the full dispensing cup was the actual dose. CONCLUSIONS: Dispensing cup markings should use a single unit of measure, and a uniform labeling system should be implemented. Teaspoon/tablespoon abbreviations should be avoided, and dispensing cup lettering should be more legible. Consumer education is essential to correct the misimpression that the full cup is always the recommended dose.