We wished to determine the predictors of the clinical course of idiopathic generalized epilepsy with grand mal seizures (IGE). We studied 70 patients with IGE. Patient information was statistically evaluated with regard to its prognostic relevance. Forty-four (63%) of the patients were seizure-free, eight despite poor compliance. Of the 26 patients who continued to experience seizures, 22 had poor compliance, and four patients did not receive the optimal dose of antiepileptic drugs (AEDs). The decisive factor in achieving seizure freedom was appropriate antiepileptic drug (AED) therapy with good compliance. The following factors were unrelated to the course of the epilepsy: sex, age at onset, duration of epilepsy, combination of different seizure types or the sequence with which various types developed, time of day during which seizures occurred, the number of seizures, and time elapsed between the first occurrence of seizures and initiation of drug treatment. Eight patients were seizure-free without AED therapy, which suggests spontaneous remission in the course of IGE. From our results, we conclude that optimal therapy with good compliance is the critical predictor for the course of IGE.