We report a longitudinal study (7-l 1 years) of a previously normal boy (MR) who presented from the age of 5 years with rare partial motor seizures and atypical ‘absences'. The history revealed a stagnation in development and speech difficulties a few months before onset of his epilepsy. The first waking electroencephalogram (EEC) showed rare generalized discharges during hyperventilation. Magnetic resonance imaging revealed an arachnoid cyst in the frontotemporal region. Although his epilepsy never became severe, he experienced important learning difficulties. Subsequent EEGs became increasingly active with left focal epileptic activity and continuous spike-waves during sleep (CSWS) present from the first sleep EEG. The first neuropsychological evaluation (7 years) showed a speech dysfluency, word finding and naming problems, inattention and low intelligence quotient. Carbamazepine was changed to clobazam and later ethosuximide was added with a rapid improvement (within 1 month) in linguistic and cognitive performances as well as in behaviour. Furthermore, the patient showed considerable progress in acquisition over the next months whereas learning to read had previously been very difficult. The epileptic activity gradually disappeared and he was able to follow regular school at an age-appropriate level. This case adds a new facet to the already recognized more obvious acquired neuropsychological disturbances known to occur in some partial childhood epilepsy syndromes with CSWS (aphasia, dementia). It manifested as prolonged insidious stagnation in learning and subtle language disability. This study documents rapid specific language improvement with change in anti-epileptic drugs and a restored immediate and long-term learning capacity, suggesting a direct but ‘hidden' role of epilepsy.