We determined if time to first remission predicts long-term antiepileptic drug response. We assessed

time to first 1-year remission (1YR) as a determinant of entering future terminal 5-year remission

(5YTR) in a population-based cohort of 144 children prospectively followed-up since their first unprovoked

seizure before the age of 16 years up to the mean age of 48 years. The proportion of patients entering

5YTR was highly dependent on the length of time to first 1YR after starting adequate treatment. For

144 patients, the overall 5YTR rate decreased from 32% for those in remission at year 1 to 24% at year 2, to

5% after 3 and 4 years, to 2% after 5 years or longer. Patients who entered 1YR within the first 5 years of

treatment had an 11-fold better chance to enter 5YTR (odds ratio = 11.4, 95% CI = 2.9–45.3, P = 0.0005)

and a 9-fold chance for uninterrupted 5YTR off medications (OR = 9.0, 95% CI = 1.171.9, P = 0.0383) compared

with those who did not enter 1YR within the first 5 years of treatment. Three additional independent

prognostic factors for predicting terminal 5YTR were confirmed: etiology, seizure frequency prior to

treatment, and seizure frequency during treatment. We conclude that delayed efficacy after starting drug

treatment gradually diminishes chances for long-term seizure remission, whether on medication or not.

Not entering remission within 5 years of starting treatment predicts failure to achieve long-term seizure

freedom in the future for the vast majority of patients.