Developmental and/or epileptic encephalopathy with spike-wave activation in sleep (D/EE-SWAS), formerly electrical status epilepticus of sleep (ESES), is a rare childhood-onset epilepsy characterized by continuous spike waves seen in sleep with or without associated seizures. D/EE-SWAS affects children ages 2-12 years and shows characteristic pattern of continuous spike-and-wave discharges during non-rapid eye movement (NREM) sleep (CSWS) on electroencephalography (EEG) with a high density of spikes. Generalized D/EE-SWAS is found in patients with acquired symptoms of progressive neurocognitive and/or behavioral regression. D/EE-SWAS with focal discharges has been reported with focal deficits. We present a 3.5-year-old boy with focal D/EE-SWAS who changed dominant handedness. He was innately right-hand dominant with obvious preference for scribbling and feeding himself with his right hand per his mother, though developed focal seizures and D/EE-SWAS of the left hemisphere and became left-hand dominant for all activities. Following medical treatment, he again used his right hand with ambidextrous handwriting. We report the first case of change in handedness with focal D/EE-SWAS. We review the available diagnostics and treatments of Landau-Kleffner syndrome (LKS) and D/EE-SWAS.