Neural cell adhesion molecule L1 (NCAM-L1/L1CAM) is a single pass transmembrane glycoprotein member of the immunoglobulin superfamily, containing six amino-terminal extracellular Ig-like domains followed by five fibronectin type-III domains. NCAM-L1 is mainly expressed in the brain, and plays an important role in the developing nervous system, with involvement in neurite fasciculation and outgrowth, myelination, neuronal migration, and neuronal cell adhesion. Mutations in the NCAM-L1 gene cause varying degrees of neurological disease including X-linked hydrocephalus, MASA syndrome, spastic paraplegia type 1, and X-linked corpus callosum agenesis, together known as L1 syndrome. Apart from the nervous system, NCAM-L1 is overexpressed in many cancers and supports a poor prognosis by facilitating aggressive tumor growth, metastasis and chemoresistance.