Ovarian hyperstimulation syndrome is an iatrogenic complication of supraphysiologic ovarian stimulation. The syndrome is al-most exclusively associated with exogenous gonadotropin stimulation and is only rarely observed after clomiphene citrate treatment or spon-taneous ovulation. C-reactive protein, an acute phase protein produced by the hepatocytes, is a marker of systemic inflammation, tissue damage, and/or infection. While the increased C-reactive protein level in the ovarian hyperstimulation syndrome made us think that there is an infection, for making this diagnosis, other infection indicators must be researched on these patients. Although the use of C-reactive pro-tein for infection in ovarian hyperstimulation syndrome is recommended, the level of C-reactive protein may increase without infection. We aimed to identify ovarian hyperstimulation syndrome with very high C-reactive protein level without infection.