Objectives: To compare the effects of intravenous calcium infusion and coasting in the prevention of the early onset ovarian hyperstimulation syndrome (OHSS) in high-risk women underwent intracytoplasmic sperm injection (ICSI). Study design: Prospective randomized trial. Patients and Methods: Sixty women at risk of ovarian hyperstimulation syndrome during ICSI cycles were randomly scheduled into two equal groups. In group I, (Intravenous calcium group), intravenous 10% calcium gluconate, 10 mL in 200 mL of normal saline (0.9%) was administered on the day of ovum pickup, days 1, 2 and 3 after ovum pickup; while in group II (Coasting group) gonadotrophins administration was ceased until serum estradiol levels checked every 24 hours, reached below 3000 pg/ mL before HCG administration. The main outcome measures were rates and grades of OHSS, and the pregnancy rate in both groups. Results: Ten patients (33.33%) in calcium group and 15 patients (50%) in coasting group developed OHSS. The incidence of mild {8 (26.67%) vs 10 (33.33%); p= 0.573}, moderate {2 (6.67%) vs 4 (13.33%); p= 0.389} and severe {Zero vs 1 (3.33%); p= 0.313} OHSS were nonsignificantly lower in calcium group compared to coasting group. The clinical pregnancy rate was nonsignificantly higher in calcium group compared to coasting group (40% vs 23.33%; p= 0.165). The mean number of retrieved (p =0.0002), metaphase II (p = 0.007) oocytes and the mean number of good-quality embryos (p = 0.0002) were significantly higher in calcium group than coasting group. Conclusions: Intravenous calcium infusion was as effective as coasting in the prevention of early severe OHSS in high-risk patients, but yielded more retrieved oocytes and higher pregnancy rates.