Objective
To evaluate outcomes from hemispherectomy and callosotomy related to the need for anti-seizure medication (ASM), seizure frequency, and cognition.

Methods
A review of the medical charts of all Danish pediatric patients who underwent hemispherectomy or callosotomy from January 1996 to December 2019 for preoperative and postoperative ASM use, seizure frequency, and cognitive data.

Results
The median age of epilepsy onset was two years (interquartile range (IQR): 0.0–5.3) for the hemispherectomy patients (n = 16) and one year (IQR: 0.6–1.7) for callosotomy patients (n = 5). Median time from onset to final surgery was 3.4 years for hemispherectomy and 10.2 years for callosotomy, while the median follow-up time was 6.9 years and 9.0 years, respectively. Preoperatively, all patients had daily seizures and were treated with ≥ 2 ASM. Hemispherectomy resulted in a reduction in seizure frequency in 87.5 % of patients, with 78.6 % achieving seizure freedom. Furthermore, 81.3 % experienced a reduction in ASM use and 56.3 % stopped all ASM. Median IQ/developmental quotient (IQ/DQ) was low preoperatively (44.0 [IQR: 40.0–55.0]) and remained unchanged postoperatively (IQ change: 0.0 [IQR: −10.0–+4.0]). Callosotomy resulted in a seizure reduction of 86–99 % in four patients, and ASM could be reduced in three patients. Median IQ/DQ was 20.0 preoperatively (IQR: 20.0–30.0) and remained unchanged postoperatively (IQ change: 0.0 [IQR: 0.0]).

Conclusion
Hemispherectomy and callosotomy result in a substantial reduction in seizure frequency and ASM use without deterioration of IQ. Extensive epilepsy surgery should be considered early in children with drug-resistant epilepsy.