Baclofen is widely used to control spasticity in children with cerebral palsy. Several publications described clinical adverse effects of baclofen oral treatment, but the effect of baclofen on seizure potentiation is still controversial. We describe a 10-year-old female patient with cerebral palsy, epilepsy, and mental retardation who developed clinical adverse effects (confusion, agitated state, insomnia, diffuse hypotonia, and hyporeflexia) and electroencephalographic (EEG) changes (quasiperiodic, generalized burst of sharp waves that take up >50% of standard EEG) during long-term oral baclofen treatment, after gradually increasing the dosage but still within the therapeutic dose. Our case showed clearly that the EEG changes in our patient, with a history of epilepsy in good control, have been induced by the baclofen increase, and we describe the possible mechanisms that could explain proconvulsive effect of baclofen.