Neuronal ceroid-lipofuscinosis is a group of neurodegenerative diseases which are characterized by an abnormal accumulation of lipopigment in neuronal and extraneuronal cells. The diseases can be differentiated into several subgroups according to age of onset, the clinical picture, neurophysiological and neuropathological abnormalities and ultrastructural studies documenting different profiles of the lipopigment. Several eponyms have been used in the designation of the diseases. Latest, an international designation abbreviated CLN has been recommended, with the addition of figures according to the subtypes. The most common type in Denmark is CLN3, also called Spielmeyer-Vogt's disease. The incidence is 1.6 per 100,000. It is characterized by slowly progressing behavioral and visual symptoms that start when the child is about four to nine years old. During the second decade of life, the disease is accompanied by seizures and severe psychomotor deterioration. Most patients die before the age of 30 years. Recently, it has been shown that this type of CLN disease is due to a mutation in a gene located on chromosome 16 (16p 12.1). A brief description of the other subtypes of CLN is given.