The objectives of this study were to investigate the lifetime prevalence of epileptic seizures in a population with acute intermittent porphyria (AIP) and to characterize the seizures and the seizure-triggering factors. A letter was sent to all patients with known AIP in Sweden registered at the National Porphyria Center (n = 294). The medical records of patients who had had epileptic seizures were reviewed in detail. The letter was answered by 268 patients (91.2%). Ten patients (3.7%) reported epileptic seizures. Eight were women (mean age 54.1 years, range 30-81 years), and 2 were men (mean age 19 years, range 9-29 years). Six patients had tonic-clonic seizures and 4 had partial seizures becoming secondarily generalized. Serum sodium levels were low in 3 patients (mean 110, range 103-120 mM), and normal in 5. Excretion of 5-aminolevulinic acid (ALA) in the urine was increased in 4 patients at the time of the seizures. In 6 patients, the seizures were associated with an acute attack of AIP (all patients with hyponatremia included). The lifetime prevalence of AIP-associated seizures was 2.2% of all those with known AIP and 5.1% of all those with manifest AIP. Epileptic seizures among persons with AIP are less common than has been previously described.