Background: Nausea and vomiting are common side effects of tramadol. We conducted a retrospective study to identify the risk factors associated with nausea and vomiting induced by intravenous (IV) tramadol patient-controlled analgesia (PCA). Methods: Four hundred and sixty-one patients who received intravenous tramadol PCA after spine surgery were enrolled in our retrospective study. Patients' demographics, total doses of tramadol administered, and types of adjuvant agents including metoclopramide pretreatment and addition of ketorolac to the PCA solution were recorded. Associations between individual variables and the IV tramadol PCA-induced nausea and vomiting were analyzed statistically. Further logistic regression analysis was used to determine the independent risk factors of each variable. Results: The independent risk factor associated with IV tramadol PCA-induced nausea and vomiting was female gender (adjusted odds ratio [OR] 2.5, 95 % confidence interval [CI] 1.4-4.6). The addition of ketorolac to PCA solution resulted in decreased nausea and vomiting (adjusted OR 0.4, 95% CI 0.2-0.7). Conclusions: Our study demonstrated that, after spine surgery, females could be associated with IV tramadol PCA-induced nausea and vomiting, and that addition of ketorolac to the PCA solution might decrease its incidence. These findings suggest that adding ketorolac to tramadol PCA solution may help in the management of IV tramadol-induced nausea and vomiting after spine surgery.