Abstract: Objective To investigate the clinical manifestations,pathogenesis and treatment of severe ovarian hyperstimulation syndrome (OHSS).Methods The clinical data of 20 OHSS patients were analyzed retrospectively. Results Severe OHSS occurred after controlled ovarian hyperstimulation for superovulation. The major manifestations of OHSS included abdominal distension,nausea,ascites,hydrothorax,oliguria,concentrated blood, acid-base and electrolytea,disturbance,azotemia,thrombosis etc.,which could be controlled by volume expansion with albumin,low-molecular-weight dextran,6% Haes,abdominal and thoracic drainages or even early pregnancy termination.Conclusion Preventive measure of OHSS is very important,and the patients must be treated timely and correctly once OHSS occurs.