Study pharmacist and hospital-physician medication histories were compared with medication orders to identify unexplained history and order discrepancies in 651 adult medicine service inpatients with 5,701 prescription medications. Discrepancies resulting in order changes were considered errors. Logistic regression was used to analyze the association of patient demographic and clinical characteristics including patients’ number of pre-admission prescription medications, pharmacies, prescribing physicians and medication changes; and presentation of medication bottles or lists. These factors were tested after controlling for patient demographics, admitting service and severity of illness.