Evidence for genetic heterogeneity in epilepsy is strong. We evaluated the concordance of clinical forms in the same family in a series of families with several cases of idiopathic epilepsy, collected as part of the Study on the Genetics of Epilepsy of the Italian League against Epilepsy (LICE). The studied families had at least three members affected by an idiopathic form of epilepsy in one or more generations. Seventy-four families (with a total of 296 affected members) have been analyzed; two families had cases with benign neonatal familial convulsions (BNFC); in 25% of the remaining families all members were affected by the same clinical form, 13.9% had a prevalent clinical form with only one affected member with a different seizure type, 36.1% had two clinical forms, and 25% had three forms of epilepsy in the same family. There are no clinical differences in the form of epilepsy between the families concordant for one clinical form and families with two or three clinical forms of id-iopathic epilepsies. The distribution of the clinical form in the affected relatives in our families showed the higher concordance with the proband in febrile convulsions (FC, 70.8%) and in epilepsy with generalized tonic-clonic sei-zures (EGTC, 63.0%). FC and EGTC were highly dif-fused in the affected relatives in the families with other forms of idiopathic epilepsy, above all in the more dis-tantly related affected family members. In our families we observed a rare association between childhood absence epilepsy (CAE) and juvenile myoclonic epilepsy (JME). In every idiopathic form of epilepsy, there was a high