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Objective: The goal of this study was to assess the complications associated with vertical parasagittal hemispherotomy (VPH), the impact of incomplete disconnection on long-term seizure freedom, and how VPH impacts cognitive development., Methods: A retrospective evaluation was performed in all patients who had undergone VPH during 1991-2022 at the authors' institution. Two-year follow-up data were available for 45 patients, and there were 6-month data for 3 more. All available postoperative MRI studies (31/48, 64.6%) were reviewed. Before 2010, postoperative MRI was only performed if seizures recurred., Results: Primary VPH led to Engel class I in 73% of patients. Acquired etiologies had a higher rate of Engel I compared to developmental and progressive etiologies (96% vs 46% and 44%, p < 0.001). Nearly half of patients (45%) showed improved cognitive trajectories as opposed to their preoperative ones, whereas in 45% trajectories remained unchanged. Additionally, 5 patients (10%) exhibited new major deficits or accelerated cognitive deterioration after VPH. Surgical complications occurred in 14 patients (29%) after the first VPH; 4 cases were classified as transient, resolving during follow-up without surgical intervention. Nontransient complications included 8 cases of hydrocephalus requiring surgical treatment, 1 shunted subdural hygroma, and 1 case of CSF leakage from the wound. Diabetes insipidus occurred in 6 patients, with all resolving spontaneously. Residual connections were present in 16 patients, primarily in the temporomesial region. Seven patients remained seizure free despite visible residual connections., Conclusions: VPH is a highly effective treatment for drug-resistant hemispheric epilepsy, resulting in durable seizure freedom and often favorable cognitive outcomes. Diabetes insipidus in addition to hydrocephalus is a common complication after VPH. Incomplete disconnection does not necessarily preclude seizure freedom.