BACKGROUND: Outpatient tympanomastoidectomy is common in many medical centers. However, failure of same-day discharge is often the result of postoperative nausea and vomiting (PONV). Many times this leads to hospital admission after tympanomastoidectomy, and it is often difficult to predict before surgery whether PONV will be an issue that impedes same-day discharge. OBJECTIVE: To determine the clinical factors correlated with the incidence of PONV requiring hospital admission after chronic ear surgery by hypothesizing that the complexity of a particular case, as measured using a 10-point scale, is predictive of surgical time or failure of same-day hospital discharge. STUDY DESIGN: Retrospective medical chart review of 103 patients having mastoidectomy with tympanoplasty for chronic otitis media over a 2-year period. METHODS: We recorded patient age, clinical data, surgical times, types of agents used for induction and maintenance of anesthesia, use of prophylactic antiemetic drugs, types and doses of analgesic agents, and PONV. Univariate and multivariate logistic regression analyses were performed to determine which variables were associated with PONV that required hospital admission. RESULTS: One third of patients studied were safely discharged from the hospital the day of surgery, and 92% were discharged within 23 hours. The most common cause for observation admission to the hospital was PONV. The only variable in multivariate analysis that significantly correlated with PONV mandating hospital admission after tympanomastoid surgery was a history of motion sickness or PONV (odds ratio, 5.21; P =.02). Although severity of disease did not correlate with length of hospital stay, it directly correlated with length of surgery. CONCLUSIONS: A history of PONV or motion sickness is predictive of PONV and length of hospital stay. Routine planning for a 23-hour overnight observation stay seems warranted for all patients undergoing tympanomastoidectomy, despite severity of disease.