Aim The aim was to determine temporal changes in increased risk of epilepsy among children with type 1 diabetes.

Methods The incidence of epilepsy up to age 15 in children with prior type 1 diabetes was analysed regarding the general Finnish child population using data from the Finnish nationwide hospital register. Type 1 diabetes and epilepsy were identified by the International Classification of Diseases 9th and 10th revision codes. Epilepsy was defined according to ILAE guidelines. The analyses were done using negative binomial regression models.

Results Preceding type 1 diabetes was diagnosed in 6162 (0.91%) of the 679 375 general children population. Incidence rate of new-onset epilepsy among children with type 1 diabetes was higher than in controls (140 vs 82 per 100 000 person-years at risk, respectively). The excess incidence diminished with time (P = 0.033 for diabetes to birth cohort interaction), from over twofold in birth cohort 1990-1993 [incidence rate ratio 2.2 (95% CI 1.7-2.9)] to 40% in birth cohort 1998-2000 [1.4 (95% CI 1.001-1.9)].

Conclusion In a population study setting, children with type 1 diabetes had an increased, but slowly declining risk of developing epilepsy. Future research may elucidate the underlying mechanisms.