70 patients scheduled for total knee arthroplasty under spinal anesthesia and a continuous femoral nerve block were randomized to spinal anesthesia with or without the addition of mini-dose morphine (0.035mg). The purpose of this study was to evaluate if there was any significant difference between groups in pain scores and opioid consumption. Patients were monitored up to 48 hours postoperatively. Results demonstrated significantly lower pain scores and tramadol consumption in the group which received mini-dose spinal morphine. The incidence of postoperative nausea and vomiting was significantly greater within the first 6 hours in the group administered the mini-dose spinal morphine.