The neuronal ceroid lipofuscinoses (NCLs) are an intriguing group of inherited neurodegenerative disorders characterized by blindness, progressive psychomotor deterioration and death of neocortical neurons. Clinically, four major NCL groups have been identified: infantile, late infantile, juvenile and adult. In recent years, our understanding of the molecular basis of different NCLs has advanced significantly. The accumulation of autofluorescent material in patients' tissues has been shown to be caused by defects in either lysosomal enzymes or in novel membrane proteins of unknown function. Although the accumulated material is biochemically well defined and some of the causative mutations are known, a unifying hypothesis for the molecular basis of the NCLs remains elusive. Further work will be required to characterize the interactiving molecules and metabolic pathways involved in the pathogenesis of NCLs.