To elucidate etiology and management of retropupillary sulcus migration of intravitreal gas after uneventful retinal detachment repair surgery. 70 year old Caucasian man presented with a temporal macula-off rhegmatogenous retinal detachment. 25-gauge (25G) pars plana vitrectomy was performed with cryopexy to retinal tear and 12% C3F8 gas tamponade under sub-Tenon's anaesthesia. At one week review, there was an elevated IOP of 28mmHg with migration of gas to the retropupillary space. Superiorly, iris was displaced anteriorly causing iridocorneal touch. There was no phacodonesis nor subluxation and retina was attached with a cryopexy scar under a 80% vitreous cavity gas fill. On treatment with topical IOP-lowering agents until two-week review, IOP had normalised to 18mmHg with persistent 50% gas fill in the retropupillary sulcus and superior iridocorneal touch.Retropupillary gas resorbed at week four with normalisation of IOP, a localised superior anterior subcapsular cataract with associated posterior synechiae, and no iridocorneal touch. Best-corrected visual acuity was 6/12 Snellen following resorption of vitreous cavity gas. Medical management may be adequate if there is no complete pupil block and adequate posterior gas fill. With complete pupil block, refractory IOP elevation, or inadequate posterior tamponade resulting in failure of retinal attachment, surgical intervention would be required.