PurposeTo investigate the effect of preoperative steroid on anatomical and functional outcomes of vitrectomy in patients with rhegmatogenous retinal detachment with associated choroidal detachment (RRD-CD), a rare but particular type of RRD.Patients and methodsThis retrospective cohort study included RRD-CD patients at Siriraj Hospital during January 2005 to December 2014. Patients with preexisting uveitis or RRD with giant retinal tears were excluded. Preoperative, intraoperative, and postoperative data were reviewed and analyzed.ResultsA total of 76 patients (76 eyes) with RRD-CD were included: 37 patients without preoperative steroid (Group A) and 39 patients with preoperative steroid for a median of 7 days (Group B: 34 patients with oral prednisolone (0.5-1 mg/kg/day) and 5 patients with 20 or 40 mg of subtenon triamcinolone). The total retinal reattachment rate at 3 months after one operation was not different between the two groups (59 vs 51%) with adjustment for confounders. The proportion of patients with visual acuity (VA) improvement at 3 months was also not different (57 vs 54%). Survival analysis revealed that 96% of redetachment cases occurred within the first 3 months and redetachment rate was not different between the two groups for up to 3 years. However, Group B showed a significant regression (partial or complete) of CD prior to operation compared to Group A (82 vs 30%, P<0.001).ConclusionPreoperative steroid significantly improved CD before vitrectomy, but seemed not to improve the single-operation retinal reattachment rate or VA at 3 months when compared to no steroid treatment in RRD-CD patients.