Pathological redundancy is defined as ignoring requests for a brief description of a topic and stubbornly following one’s own preconceived ideas. Clinically, there are many diseases that cause pathological redundancy, and one of the more common is mental retardation. Experts say, mental retardation caused by pathological redundancy patients need to be diagnosed and treated as soon as possible to avoid aggravation of the condition. Mental retardation caused by pathological redundancy diagnosis is as follows: First, the diagnostic criteria 1, intelligence is significantly lower than the average level of people of the same age, in the individual intelligence test intelligence quotient (IQ) is lower than the population mean two standard deviations, generally speaking, the IQ in the 70 or less. 2. Inadequate social adaptability, as evidenced by significant deficits in the ability to live individually and fulfill social responsibilities. 3. The onset of the disease is before the age of 18. To make a diagnosis of mental retardation, the above three conditions must be present, and one of them is indispensable, that is to say, only the intellectual development is insufficient or the IQ is low but not the ability is not low, it cannot be diagnosed. On the other hand, those who have social adaptive ability but not low IQ cannot be diagnosed, and any intellectual regression after 18 years of age cannot be diagnosed as mental retardation but should be called dementia. For all diagnosed patients, aetiological diagnosis should be made through history and physical examination, genetics, metabolism, endocrinology and other laboratory tests, as well as special cranial examination. For those with unknown etiology, chromosome examination should be done routinely for karyotype analysis.