BACKGROUND: Stereoelectroencephalography (SEEG) has been shown to be a valuable tool for the anatomoelectroclinical definition of the epileptogenic zone (EZ) in patients with medically refractory epilepsy considered for surgery (RES patients). In Spain, many of those patients are not offered this diagnostic procedure. OBJECTIVE: To evaluate the effectiveness, safety, and cost-effectiveness of SEEG to define the EZ in RES patients compared to no SEEG intervention, ie, remaining with further antiepileptic drugs. METHODS: We undertook a systematic review with meta-analyses on the effectiveness and safety of SEEG. A cost-effectiveness analysis was conducted using a Markov model, which simulates the costs and health outcomes of individuals for a lifetime horizon from the perspective of the Spanish National Health Service. The effectiveness measure was quality-adjusted life years (QALYs). We ran extensive sensitivity analyses, including a probabilistic sensitivity analysis. RESULTS: The EZ was found in 92% of patients who underwent SEEG (95% confidence interval [CI]: 0.87-0.96); 72% were eligible for epilepsy surgery (95% CI: 0.66-0.78) and 33% were free of seizures after surgery (95% CI: 0.27-0.42). Of the patients who underwent surgery, 47% were free of seizures after surgery (95% CI: 0.37-0.58). Complications related to implantation and monitoring of SEEG and the subsequent intervention occurred in 1.3% of patients (95% CI: 0.01-0.02). In the base case analysis, SEEG led to higher QALYs and healthcare costs with an estimated incremental cost-effectiveness ratio of 10 368 EUR per QALY (95% CI: dominant-113 911), making the probability of cost-effectiveness between 75% and 88%. Further sensitivity analyses showed that the results of the study were robust. CONCLUSION: SEEG is a cost-effective technology in RES patients when compared to no SEEG intervention.< Réduire