SummaryObjectiveThis study aimed to identify early clinical, magnetic resonance imaging (MRI), and electroencephalographic (EEG) characteristics of neuronal ceroid lipofuscinosis type 2 (CLN2) disease to enable early diagnosis, thus providing the key to early treatment, and optimized care and outcomes.MethodsRetrospective clinical chart review of a series of patients diagnosed with CLN2 disease from 2005 to 2015 at a single center in Italy. Clinical, MRI, and EEG findings were reviewed.ResultsA total of 14 patients were included. For the whole group, median (range) age at disease onset was 3.0 (2.0–3.8) years. Epilepsy was the most commonly reported presenting symptom (in 50% [seven of 14] of patients), occurring at the age of 3.2 (2.6–3.8) years. First seizure was myoclonic in 36% (five of 14) of patients, followed by generalized tonic–clonic in 29% (4 of 14), atonic in 22% (three of 14), and focal with motor signs in 14% (two of 14). All patients walked independently at the age of 12.0 (11.0–18.0) months, but delayed speech or regression of acquired verbal skills was present in 100% of patients at 3 years. EEGs revealed a photoparoxysmal response (PPR) on intermittent photic stimulation in 93% (13 of 14) of patients. PPR was present from the first EEG, which was performed at 3.6 (3.1–4.0) years, in 43% (six of 14) of patients; it was documented at low (1–3 Hz) stimulation frequencies in 69% (nine of 13) and took the form of a flash‐per‐flash response in 69% (nine of 13). First brain MRI at the age of 3.8 (3.0–5.1) years revealed cerebellar atrophy in 100% (14 of 14) of patients and alteration of the periventricular white matter signal in the posterior hemispheric region in 79% (11 of 14).SignificanceEarly photosensitivity (typically PPR at low stimulation frequencies of 1–3 Hz) is a hallmark of CLN2 disease. This diagnosis should be considered in a child presenting with any type of seizure, and particularly if it is accompanied by delayed speech and/or ataxia or MRI abnormalities (posterior white matter signal alteration or cerebellar atrophy).