Mental retardation and developmental delay are not equivalent, so there are differences in definitions, causes and clinical manifestations. 1. Definition: Mental retardation refers to organic damage to the brain or incomplete brain development. Developmental delay refers to the slow speed or abnormal sequence of the normal development process. 2. Pathogenesis: Mental retardation is generally due to brain damage or incomplete brain development, resulting in persistent disorders of cognitive and mental activities, mostly due to brain malformations, endocrine abnormalities, poisoning and infection, or genetic variations. Developmental delay is associated with chromosomal abnormalities, metabolic diseases, and bone diseases. 3. Clinical manifestations: Mental retardation is characterized by the failure of the brain to develop normally or the stagnation of intellectual activities at a relatively low stage. Developmental delay is characterized by backwardness in physical, motor, language and intellectual development. Whether it is developmental delay or mental retardation, it is recommended to consult a doctor in time, follow the doctor’s instructions for further examination, clarify the cause with the doctor’s help, and actively cooperate with the doctor in handling or treating the condition.