A generalized tonic seizure is a type of generalized motor seizure characterized by bilateral limb stiffening or elevation, often with neck stiffening without a subsequent clonic phase. The tonic activity can be a sustained abnormal posture, either in extension or flexion, sometimes accompanied by tremor of the extremities. The phenotype is Human Phenotype Ontology entry HP_0010818 (Generalized tonic seizure). Also known as: Generalised hypertonic seizure, Generalised tonic seizure, Generalised tonic seizures, Generalized hypertonic seizure, Generalized tonic seizures.