Tay-Sachs disease (a GM2 gangliosidosis) is an inherited neuronal storage disease that can affect individuals across the age spectrum. Psychosis is reported in 30% to 50% of adult-onset patients, and many are misdiagnosed with schizophrenia. Mood disorders are present in more than 25% and cognitive impairment in more than 20%. Treatment of psychosis with neuroleptics may not have a favorable risk/benefit ratio, but treatment with benzodiazepines or electroconvulsive therapy may be efficacious. Metabolic diseases such as gangliosidosis are probably under-recognized as causes of neuropsychiatric illness. Increased awareness of these disorders will lead to accurate diagnosis, appropriate treatment selection, and genetic counseling.