Subperiosteal orbital abscess (SPA) is a serious complication of paranasal sinusitis, which can lead to blindness or even death. A quick response is necessary as this condition is treatable. Early surgical intervention is indicated if there is risk of visual loss, or if no improvement is observed within 48 hours of starting medical therapy. Three patients with orbital SPA secondary to sinusitis treated successfully by Functional Endoscopic Sinus Surgery (FESS) are presented in this case series. The surgical indications were impending visual loss with an abscess and cellulitis impinging on the optic nerve in one child and in the other two patients, a lack of clinical response within 48 hours after starting systemic antibiotic. CT scans, nasal endoscopy, and ophthalmologic examinations are mandatory during the evaluation process. The advantages of FESS in these patients were the avoidance of external ethmoidectomy and its external facial scar, an early drainage of the affected sinuses, SPA, and the eradication of the disease from the fronto-ethmoidal region leading to an enhanced recovery and a reduced hospital stay. FESS is also a safe, convenient and minimally invasive procedure in patients presenting with serious complications of sinusitis.