The clinical presentation of hyperreactio luteinalis can mimic ovarian hyperstimulation. Historically, though, the former most often leads to unnecessary surgery whereas the latter is treated supportively. We present a case of a 32-year-old woman who was initially seen with markedly enlarged multicystic ovaries, ascites, and pleural effusions in the tenth week of a spontaneously conceived gestation. Despite a noniatrogenic cause, the patient received supportive management, as would be given with ovarian hyperstimulation syndrome. Making the distinction between hyperreactio luteinalis and ovarian hyperstimulation syndrome has important consequences for diagnosis and management. (Am J Obstet Gynecol 1997;176:1300-4.)