Late infantile neuronal ceroid lipofuscinosis (Jansky-Bielchowsky disease) is a rare disease caused by mutations in the CLN2 gene. The authors report the clinical outcome and correlate with genotype in 12 Spanish patients with this disease. Psychomotor regression, epilepsy, and other clinical symptoms/signs were assessed. Age at onset of clinical symptoms ranged from 18 months to 3.7 years, and they included delayed speech and simple febrile seizures followed by epilepsy. Partial seizures and myoclonic jerks occurred at an earlier age (median 3.4 and 3.7 years, respectively) than ataxia and cognitive decline (median 4 years). Clinical regression was initiated by loss of sentences (median 3.7 years) followed by loss of walking ability and absence of language (median 4.5 years). Patients showed blindness and lost sitting ability at similar age (median 5 years). The authors report 4 novel mutations in the CLN2 gene. This study provides detailed information about the natural history of this disease.