The syndrome of continuous spike-waves during slow sleep (CSWS) is considered an epileptic encephalopathy in which the epileptiform abnormalities may contribute to progressive cognitive dysfunction. The characteristic electroencephalographic feature of the syndrome occurs during non-REM sleep, and takes the form of continuous bilateral and diffuse slow spike-waves that persist through all slow sleep stages. Using a case study design including clinical, neuropsychological, electroencephalographic, and positron emission tomography with 18F-fluorodeoxyglucose (PET-FDG) investigations, we describe the clinical and electroencephalographic findings in two patients who presented with nonsymptomatic epilepsy with unilateral spike-waves during sleep. Both patients presented with a left unilateral motor neglect of the upper limb that was associated with unilateral CSWS activity over the right hemisphere, predominantly in the centrotemporal region. PET-FDG studies during the active phase of CSWS showed right centrotemporal hypermetabolism in both cases. After treatment, a regression of the CSWS activity and an improvement of the cerebral FDG pattern were paralleled by a remission of the motor neglect. These cases demonstrate that the electroencephalographic pattern of CSWS in nonsymptomatic epilepsies is not necessarily diffuse and bilateral, and that focal unilateral CSWS activity can be associated with focal neuropsychological deficits. These findings add further evidence that the spectrum of clinical conditions associated with the electroencephalographic pattern of CSWS can include different forms of acquired cognitive disturbances that may be focal in nature.