Ovarian hyperstimulation syndrome (OHSS) is one of the most common iatrogenic complications induced by assisted reproductive technology. Hydrothorax develops in about 10 percent of patients with severe OHSS and it is usually associated with marked ascites. On the other hand, severe hydrothorax without marked ascites is uncommon, and its pathogenesis remains unclear. We recently experienced a case of severe unilateral hydrothorax with minimal ascites induced by quintuplet pregnancy following intrauterine insemination with controlled ovarian hyperstimulation. Severe hydrothorax was resolved after only conservative and symptomatic management without invasive procedure such as thoracentesis or paracentesis. We report this case with brief review of literature.