<p>Data on the manifestation and progression of neurological and psychiatric symptoms in adult patients with late-onset Tay-Sachs (LOTS) disease after the age of 2&#xa0;years are scarce and not available for Germany. In this cross-sectional study data from the “8 in 1” register study for gangliosidoses of 16 adult patients with LOTS were retrospectively evaluated with respect to the manifestation and the occurrence of neurological and psychiatric symptoms. The LOTS can be manifested in preschool age with a&#xa0;neurodevelopmental disorder, in school age and adolescence with cerebellar symptoms or in adolescence and adulthood with leg dominant muscle weakness and muscle atrophy in the sense of a motor neuron disease (MND). The initial symptoms of LOTS begin insidiously, are variable and often go unrecognized. Severe psychiatric disorders regularly occur in the course of the disease, particularly in those patients who have neurological developmental disorders and manifestation of cerebellar symptoms. The prevalence of psychiatric disorders is 62.5%. In 10 of the 16&#xa0;adult patients, psychoses occurred that were diagnosed as severe depression, bipolar affective disorder, as polymorphic psychotic disorder or as schizoaffective disorder. The patients were treated in particular with atypical antipsychotic drugs, benzodiazepines and mood stabilizers. Neuropsychiatric symptoms in LOTS were explained with the concept of a cerebellar cognitive affective syndrome (CCAS) as an organic brain disease of the cerebellum; however, symptoms such as massive psychomotor agitation, anxiety, rapid mood swings, confusion, formal and content-related thought disorder as well as hallucinations cannot be completely explained by CCAS and are consistent with concepts that describe a role of cerebellar network dysfunctions in psychoses. Our data can help to include LOTS as a&#xa0;differential diagnosis in patients with psychiatric and neurological symptoms.</p>