Patients with Sturge-Weber syndrome often present with seizures during the first year of life. Currently, only patients with clinically significant seizures who do not respond to medical treatment are candidates for early epileptic surgery. However, a delay of surgical treatment may result in cognitive deterioration. We studied the correlation between parameters and outcome of seizures to re-examine the criteria for early epilepsy surgery. We performed a retrospective chart review combined with telephone interviews of parents of all Israeli infants with unilateral Sturge-Weber syndrome and early onset seizures, and we examined whether age of seizure onset and seizure intensity were correlated with cognitive level and the degree of hemiparesis at follow-up. We recruited a total of 15 patients with unilateral Sturge-Weber syndrome and early onset seizures, five of whom underwent epilepsy surgery. The mean follow-up period of all the patients was 15 years: six patients had normal intelligence, four had borderline cognitive level, three had mild mental retardation and two had moderate mental retardation. Eight of the ten non-operated patients still experience seizures at follow-up. Cognitive delay was significantly correlated with seizure intensity in the early period, but not with the age of seizures onset, the degree of hemiparesis, or the presence of ongoing seizures. We conclude that high seizure intensity in young patients with Sturge-Weber syndrome is a prognostic marker for mental deterioration.