Background: The modified endoscopic Lothrop (MELP) or Draf III procedure can provide extended endoscopic access to the frontal sinus. The ability to access the entire frontal sinus entirely endoscopically is often debated and there is little published data to predict access based on tumor location. Methods: MELP was performed in 10 cadaver heads. Access was defined as the ability to contact the bone under vision with the head of a 70-degree diamond burr. Access was assessed in 3 areas: the orbital roof and the anterior and posterior walls of the frontal sinus. Endpoints were defined in millimeters from medial orbit and lateral quartile zones. Results: Complete lateral access was excellent anterior and posterior in 95% of sinuses (mean 15.5 ± 7.8 mm and 15.4 ± 7.7 mm, respectively). Access to the orbital roof was limited (10.3 ± 4.6 mm; p = 0.01 comparing anterior and posterior). For sinuses pneumatized beyond the midorbital point, only 10% of lateral orbital roofs were contacted. Orbital roof access correlated with the anteroposterior (AP) distance between the olfactory fossa and outer periosteum of the frontal beak (r = 0.6, p < 0.01). Conclusion: Lateral endoscopic access to the walls of the frontal sinus is excellent except for the sinus floor. Access to the orbital roof is reliable in the medial quarter only and minimal lateral to the midorbital point. The ability to predict the areas accessible by the endoscopic approach and those areas that might require ancillary approaches is important for both surgical planning and patient expectations.