Background: Spinal anesthesia is an effective regional anesthesia technique, which is preferred in almost 86% of cesarean sections in the United States and United Kingdom. Eighty percent of cesarean sections done at the Aga Khan University hospital are under spinal anesthesia. Shivering is a common complication of spinal anesthesia, it occurs in 40%-64% of patients after neuraxial anesthesia. Shivering may cause maternal and fetal hypoxemia, maternal discomfort and a problem to the anesthesiologists when it comes to monitoring the patient during cesarean sections. Ondansetron a 5-HT3 receptor antagonist is effective in treatment and prevention of post spinal anesthesia shivering. In published studies use of a fixed dose in patients with different weights, masked the dose effect ondansetron in preventing shivering. Such that not adjusting the dose according to the weight of patients’ resulted in a higher occurrence of shivering. No study compares different doses of ondansetron in preventing shivering in parturient women who have had spinal anesthesia for cesarean section. Objectives: To determine if a weight-adjusted dose is better than a fixed dose of ondansetron in preventing shivering following spinal anesthesia for cesarean delivery. Study design: Double blinded Randomized Controlled Trial. Method: This is a randomized, double-blinded controlled trial of 124 women scheduled for elective cesarean surgery. The Women were randomized into two equal groups. The intervention group received intravenous ondansetron weight adjusted dosing at 0.1mg/kg and the control group received a fixed dose of 4mg before spinal anesthesia. The occurrence and severity of shivering and other outcomes, such as headache, pruritus were assessed and recorded during the surgery and postoperative period. Results: A total of 124 patients were included in the study. Social demographic data and baseline vital signs did not differ significantly between the groups. Shivering was observed in 14 patients (22.6%) in the control group that received 4mg ondansetron and 7 patients (11.3%) in the intervention group that had 0.1mg/kg of ondansetron, but there was no statistical difference between the groups (p- value 0.090). The severity of shivering was greater in the control group compared to intervention group where patients who developed grade two shivering were 8.1% to 0% respectively. (P value 0.047). There was no difference in the occurrence of pruritus between the two groups. No patient developed a headache or required treatment for very severe shivering. Conclusion: This study, found that Ondansetron weight adjusted dose at 0.1mg/kg, reduced the severity of shivering when compared to