Bilateral perisylvian polymicrogyria (BPP) is a neurological disorder that affects the cerebral cortex (the outer surface of the brain). The cerebral cortex of the brain normally consists of several deep folds and grooves. In BPP, the grooves that develop during embryonic growth form improperly on both sides of the brain near the Sylvian fissure, resulting in an increased number of folds that are unusually small. Signs and symptoms typically become apparent at birth, infancy, or later during childhood, and may include partial paralysis of the face, tongue, jaw, and throat; problems with speech and swallowing; excessive drooling; and seizures. Mild to severe intellectual disability often is also present. Some people with BPP have other health problems or birth defects. Most cases of BPP occur sporadically in people with no family history of BPP. Rarely, more than one family member has BPP, and the pattern of inheritance depends on the cause. Genetic causes may include genetic changes in single genes and contiguous gene disorders such as 22q11.2 deletion syndrome. BPP has also been reported in association with twin pregnancy complications. The diagnosis of BPP is based on the symptoms present and a thorough neurological evaluation including various imaging techniques.