In this paper, we present the design of an epilepticseizure detector. This circuit is part of an implantable device used to continuously record intracerebral electroencephalographic signals through subdural and depth electrodes. The implemented seizure detector is based on a detection algorithm validated in Matlab tools and the circuits were implemented using CMOS 0.18-microm process. The proposed system was tested using intracerebral EEG recordings from two patients with drug-resistant epilepsy. Four seizures were assessed by the proposed CMOS building blocks and the required delays to detect these seizures were 3, 8, 11, and 11 sec, respectively after electric onset. The simulated total power consumption of the detector was 6.71 microW. Together, these preliminary results indicate the possibility of building implantable ultra-low power seizure-detection devices.