Mental retardation
F70 Mild mental retardation
F71 Moderate mental retardation
F72 Severe mental retardation
F73 Profound mental retardation
F78 Other mental retardation
F79 Unspecified mental retardation

A fourth character may be used to specify the extent of associated behavioural impairment:
F7x.0 No, or minimal, impairment of behaviour
F7x.1 Significant impairment of behaviour requiring attention or treatment
F7x.8 Other impairments of behaviour
F7x.9 Without mention of impairment of behaviour