Background: Since the introduction of concept of endoscopic sinus surgery, it has become clear that “frontal recess" or outflow tract of the frontal sinus is the key area in pathogenesis of frontal sinusitis and frontal sinus disease still poses a significant challenge to most of the endoscopic sinus surgeons. Objective: To study the anatomical variations of the frontal recess and to evaluate its surgical importance in frontal sinus problems. Patients and methods: This is a clinical trial prospective study approved by ENT department of Al Hussein University Hospitals and included 50 Egyptian patients selected from ENT outpatient clinic at Al Hussein University Hospitals and Banha teaching hospital between June 2017 and January 2021. The study included patients suffered from chronic frontal sinus problems refractory to medical treatment.  All patients underwent to complete history, general examination, ENT examination and multislice CT nose & PNS. The CT scan of all patients was reviewed for the following findings: Prevalence and size of Agger nasi cells, Uncinate process, Frontoethmoidal air cells and Anteroposterior diameter of frontal sinus ostium. Endoscopic frontal sinusotomy was done by uncapping egg technique (Draf type 2a) by a single surgeon for all patients. Intra-operative evaluation including: the time of frontal sinus surgery (on each side), easiness of surgery (using visual analogue scale from 1-10 score according to surgeon questionnaire), and external work ( trephine or osteoplastic flap) needed or not?. Results: In this study we found that the agar nasi cell were present in 45 patients (90%), which were further divided into bilateral sides in 35 patients (70%) and unilateral in 10 patients (20%) with total number of sides (80) in coronal, axial and sagittal cuts. The size of agar nasi cells was and classified these sizes in 3 groups. Small group ranging from < 500 mm3 found in 10 sides representing 10%. Medium sized group ranging from 500 – 3000 mm3 in 70 side representing 70%. Large agar nasi cell group with a size bigger than > 3000 mm3 found in 5 sides of this group representing 5% of all sides. On surgery, we found that in absent agar nasi cell 5 sides were easy (25%), 10 side were difficult (50%) and 5 sides were very difficult (25%). In small sized agar nasi cells we found that 3 sides were easy in operation (60%), 1 side were difficult (20%) and 1 sides were very difficult (20%). In medium sized agar nasi cells, we found that all sides were easy (100%). In large sized agar nasi cell all sides were easy (100%). These results indicated that on increase the size of agar nasi cell, surgery becomes easy and on decrease the size of agar nasi cell, surgery is more difficult. A large agger nasi cell (ANC) offers a greater potential to facilitating the approach to the frontal sinus because of the extensiveness of the frontal recess (FR). Conclusion: The frontal recess is a potential space that is routinely occupied by a number of different frontal recess cells which can act like a “cork in a bottle" to cause frontal sinus obstruction. Endoscopic sinus surgery of frontal recess area should be undertaken by experienced and well-trained surgeons only.