The diagnosis of children with intellectual disabilities is aimed not so much at comparing the level of their development with age standards and the degree of lagging behind healthy children, as it is intended to determine the initial level of their intellectual development, to note the successes achieved at certain stages of rehabilitation, to show the areas of activity that the child can engage in, to determine his potential and thereby to indicate the priority areas in rehabilitation work. The complexity of psychological diagnosis of such children lies in the fact that intellectual disorders are caused by a violation or underdevelopment of many functions, therefore they can be a consequence of damage to any of them. Errors in diagnosis can lead to the choice of an overestimated or underestimated psychological and pedagogical rehabilitation program, which leaves neither the teacher nor the child any hope for tangible results.