Background: Opioid analgesics are widely used to reduce postoperative pain and to enhance post-operative recovery. However, orthostatic intolerance (OI) induced by opioid containing intravenous patient controlled analgesia (IPCA) may hinder postoperative recovery. This study investigated factors that affect OI in patients receiving IPCA for postoperative pain control. Methods: OI was instantly evaluated at the time of first ambulation in 175 patients taking opioid containing IPCA after open and laparoscopic subtotal gastrectomies. Patients were classified as having OI if they experienced dizziness, nausea/vomiting, blurred vision, headache, somnolence and syncope. Factors contributing to OI were assessed with logistic regression analysis. Results: Out of 175 patients, 61 (52.6%) male and 44 (74.6%) female patients experienced OI at the time of first ambulation. The frequency of OI related symptoms were dizziness (97, 55.4%), nausea (46, 26.3%), headache (9, 5.1%), blurred vision (3, 1.7%) and vomiting (2, 1.1%). Significant risk factors for OI were gender (P=0.002) and total amount of opioids administered (P=0.033). Conclusions: The incidence of OI is significantly higher in male than in female patients and is influenced by the opioid dose.