Severe ovarian hyperstymulation syndrome is a rare but potentially life-threatening complication in patients undergoing assisted reproductive techniques (ART). The pathogenesis of this condition is likely to be multifactorial. The aim of the retrospective study was to present management in moderate and severe iatrogenic ovarian hyperstymulation syndrome (OHSS) in clinical material. The study group was 19 women, admitted to the Department of Obstetrics and Gynecology in Central Clinical Hospital of Ministry of Interior and Administration in Warsaw from large outpatient infertility center "Novum" in Warsaw with moderate and severe OHSS between 14.07.2004 and 8.11.2005. Laboratory tests and ultrasound examination of the ovarian size and ascites were performed, abdominal circumference was measured. Patients were treated with rehydration with intravenous crystalloids and colloids, diuretics, antibiotics, anticoagulants and ultrasound-guided paracentesis if symptoms of ascites become severe (ascites causes pain and compromised pulmonary function). Oral intake of water was restricted, monitoring of fluid intake and output, and daily monitoring of body weight was performed. During treatment controlled laboratory tests were done. In one patient occurred intra-abdominal hemorrhage from ovarian rupture and laparotomy with oophorectomy was performed. The ovarian hyperstimulation syndrome is still a difficult diagnostic and therapeutic problem and more studies are required to elucidate pathophysiology of OHSS. Because of still unknown etiology treatment is empirical and in most of cases bases on experience of medical team. Thus, the management in individual patients varies according to the severity of ovarian hyperstymulation syndrome and its complications