The symptoms typically begin between the ages of three and seven years although the condition may rarely occur in children as young as 18 months of age. Affected children often appear to have acquired deafness since they fail to respond to verbal language and in some cases to nonverbal sounds. A significant minority of children with LKS also develops serious behavioral dysfunction, including hyperactivity, temper outbursts, or withdrawn behaviors but rarely the severe social impairments seen in autism spectrum disorders.

Approximately 70% of affected children have obvious seizures, most often focal with or without alteration of awareness and/or atypical absence in type.