Orbital floor fractures commonly occur just medial to the junction of the infraorbital nerve and the inferior orbital fissure because the bone is thinner posteromedial to the infraorbital nerve than that lateral to the nerve. The authors previously reported 2 pediatric patients with an isolated orbital floor fracture lateral to the infraorbital nerve. The authors showed that, on the unaffected side of these patients, the lateral portion of the orbital floor was thinner than the medial portion. In the present study of 5 adult patients with an isolated orbital floor fracture lateral to the infraorbital nerve, the authors compared the thickness of the medial and lateral portions of the orbital floor with that of the infraorbital nerve on the unaffected side. Computed tomographic images showed that the bone lateral to the infraorbital nerve was somewhat thinner than bone in the medial portion. Because the orbital structures are generally symmetrical, our findings suggest that these 5 patients had partial anatomical weakness in the lateral portion of the infraorbital nerve on the affected side, resulting in an isolated orbital floor fracture lateral to the infraorbital nerve.