Ovarian Hyperstimulation Syndrome (OHSS) is a condition that can occur in women undergoing in vitro fertilization, after having follicle stimulation hormone (FSH) injections to stimulate egg growth and maturation. Some patients respond excessively to the drug and dose given. If large numbers of eggs mature, the high hormone levels combined with the increased size of the ovaries, can cause extreme, and sometimes lethal, side effects. The pathophysiology, prevention and management of this syndrome have been revolutionized over the past decade and it is important for reproductive practitioners and infertility specialists to understand the latest findings about this potentially deadly condition. The author reviews in depth the important classification, epidemiology, pathophysiology, complications and prediction, prevention and treatment options for this pathology. This book is intended for infertility specialists, reproductive medicine specialists and assisted reproduction specialists.