We herein present the case of a postoperative orbital fluid accumulation in a 1.5-year-old boy masquerading as subperiosteal orbital abscess (SPA). The patient was admitted to our hospital under the impression of orbital cellulitis with SPA. He subsequently underwent endoscopic sinus surgery and received external drainage for decompression. A significant amount of fetid odor abscess was drained from the subperiosteal space. However, a new episode of eyelid swelling was noted 1 week after the operation. Furthermore, a sinus computed tomography showed a very similar picture of the swelling compared with the preoperative image. Under the impression of recurrent SPA, a second operation was then performed. This time, however, only a small amount of granulated tissue and serosanguineous fluid was found. No microorganisms were cultured from this tissue/fluid, which ruled out any possible infection. It is thus a challenge to establish a differential diagnosis between postoperative fluid accumulation and SPA.