BACKGROUND Sympathetic ophthalmia (SO) is a bilateral diffuse uveitis that can arise after ocular trauma or ocular surgery in the inciting eye. Pars plana vitrectomy (PPV) is one of the risk factors for SO. Several reports have described SO developing after 23- and 25-G PPV, but none have described SO occurring after 27-G PPV. We describe herein a case of SO after 27-G PPV for rhegmatogenous retinal detachment. METHODS A 42-year-old woman presented with visual disturbance in the right eye. Best-corrected visual acuity (BCVA) was 6/200 in the right eye. Fundus examination revealed off-macula retinal detachment with retinal tears at both ends of retinal lattice degeneration at the temporal-oven peripheral retina of the right eye. We therefore performed 27-G sutureless PPV on the right eye. After 12 days, the retina was reattached, and BCVA improved to 6/30 in the right eye. Fifteen days postoperatively, she experienced headache and reduced vision in both eyes. Symptoms gradually worsened, and she visited our hospital 21 days postoperatively. BCVA was 6/30 in the right eye and 6/15 in the left eye. Slit-lamp examination revealed uveitis in the anterior chambers of both eyes, and fundus examination showed papillitis and subretinal detachment at the posterior poles of both eyes. Optical coherence tomography revealed subretinal fluid in the maculae of both eyes and fluorescein angiography showed multiple hyperfluorescent leakage sites in the retinal pigment epithelium. Cerebrospinal fluid examination showed pleocytosis and human leukocyte antigen testing showed expression of the DR04 phenotype; therefore, the patient was diagnosed with SO. She was treated with steroid therapy, and her visual disturbance subsided and the subretinal fluid improved as well. Her BCVA was 6/15 for the right eye and 6/5 for the left eye 93 days after the initial surgery. CONCLUSIONS The present case shows that even if the sclerotomy site of 27-G PPV is small, there is still a risk of SO occurring in the eyes of patients who underwent transconjunctival vitrectomy. Ophthalmologists should recognize SO as complication of 27-G PPV and carry out proper management as early as possible.