The neuronal ceroid lipofuscinoses (NCLs) collectively constitute the most common group of progressive brain diseases in children. The childhood forms of NCL are recessively inherited monogenic diseases, resulting in progressive dementia and motor problems, epilepsy, blindness and, finally, early death. Pathologically, the NCLs are characterized by accumulation of autofluorescent storage material in the lysosomes of neurons and other cells. The disease is selectively manifested in the central nervous system, so that there is a progressive loss of neurons. This leads to a dramatic cerebral atrophy typical of the early onset forms of NCL. The present review summarizes the knowledge of the biochemistry of NCLs, and discusses the possible pathogenetic mechanisms involved in the neurodegeneration in NCLs.