Lens subluxation can be caused by many conditions including Marfan syndrome and other hereditary conditions, and blunt trauma. Lens displacement can cause pupillary block and angle closure. This is commonly misdiagnosed as primary angle closure glaucoma (PACG), which can lead to a delay in lens surgery. This study investigated the outcomes of lens surgery in patients with lens subluxation misdiagnosed as PACG. The type of lens surgery was determined by the extent of zonular dialysis. Trabeculectomy was carried out in cases where angle closure was more than two quadrants. Of the total of 2054 patients initially diagnosed with PACG, 85 (4.1%) were re-diagnosed as glaucoma secondary to lens subluxation. Lens surgery was associated with improvements in visual acuity, reduced IOP and increased anterior chamber depth. The more angle-closure quadrants and longer delay to surgery were risk factors for poor postoperative IOP control. Misdiagnosis and inappropriate initial therapy resulted in long-term angle closure and poor IOP control, with resultant persistent damage to the trabecular meshwork and optic nerve. Therefore early and accurate diagnosis is very important in the prognosis of lens subluxation. The authors advocate the use of ultrasound biomicroscopy (UBM) in all patients initially diagnosed as PACG.