Choroidal detachment is an uncommon but serious complication of pars plana vitrectomy (PPV) with 20 gauge Claes cannula system. The purpose of this study is to document this rare complication.Seventy year old male patient was operated due to dropped IOL. During retrobulbar anesthesia subconjunctival hemorrhage and chemosis occured. Then 23 gauge infusion line was inserted at inferior temporal margine and opened. 20 gauge Claes cannulas were inserted and pars plana vitrectomy was started but the choroid was seen to be detached from inferotemporal quadrant. Changing the placement of the infusion cannula was not easy due to the hypotony of the globe. Perfluorocarbon liquid was used to fill the vitreous cavity. We used superotemporal cannula for the infusion. Cannulas were unstable due the conjunctival edema which was a complication of retrobulbar anesthesia. Another sclerotomy was opened to stabilize the infusion cannula. At the end of the operation the IOL was moved from the posterior chamber into the sulcus and the globe was filled with the silicone oil.We think that the patient had a detached choroid and it was re-attached but it detached again and the second detachment was bigger than the first one.Though we saw the tip of the infusion canulla at the beginning of the surgery, and it was confirmed that it was in the vitreous cavity, conjunctival edema may have pushed it back to choroidal level. We suggest to change the approach to open sclerotomy, instead of cannula insertion system, when an anesthesia complication occurs that is threatening the stabilisation of the infusion cannula.