PURPOSE: The frequency and popularity of immediate sequential bilateral cataract surgery (ISBCS) is increasing. We discuss the course of rehabilitation for a patient who underwent ISBCS and developed toxic anterior segment syndrome (TASS) in both eyes. METHODS: This study is a case report. RESULTS: The patient was a 42-year-old woman with no remarkable past medical history who underwent ISBCS at another hospital in 2023. Intraoperatively, mitomycin C (MMC) was inadvertently instilled into the anterior chamber of both eyes at the conclusion of surgery instead of carbachol (Miostat®). The next day, the patient noticed vision loss, and an ophthalmological examination revealed corneal edema in both eyes. She was referred to our hospital with the diagnosis of bilateral TASS. Although the left eye began to improve after a week of medical treatment, the right eye finally required Descemet's membrane endothelial keratoplasty. At the 2-month postoperative visit, uncorrected distance visual acuity was 0.7 bilaterally, and both corneas were clear on slit lamp biomicroscopy. CONCLUSION: Although ISBCS provides convenience in many areas, we believe that it should be performed only for particular indications and conditions, because it may lead to severe problems such as bilateral blindness.