Enophthalmos previously has been reported to be a rare complication of maxillary sinus mucoceles. We report three patients treated by the senior author (T.C.C.) over a 2-month period for enophthalmos or obvious deformity of the midface associated with complete opacification of the maxillary antrum. Most previous authors have stressed the role of chronic pressure necrosis or osteitis leading to bone destruction, with primary involvement of the orbital floor. No patients in this series had symptoms typical of maxillary sinus mucoceles. Two of our three patients presented with minimal symptoms of chronic infection. There was inward collapse of the anterior, superior, lateral, and medial walls of the maxillary sinus, with no radiographic or intraoperative confirmation of bone destruction. We speculate that this process may be the result of chronic maxillary hypoventilation with subsequent atelectasis of the antrum secondary to chronic negative pressure. All patients had obstruction at the osteomeatal complex and were treated by endoscopic enlargement of the natural maxillary ostium.