We describe the case of a 36 old woman with a right massive hydrothorax resulting from Controlled Ovarian Hyperstimulation (COH) for infertility. This complication is defined as Ovarian Hyperstimulation Syndrome (OHSS) which usually includes abdominal pain, nausea and ascites, rarely involving the respiratory apparatus. The usual determining factors of OHSS are the presence of high serum estradiol levels and pregnancy. In the case that we describe the serum estradiol levels during COH were monitored and were slightly higher than the COH alarm threshold and the patient was not pregnant.