The two classifications are similar and both include:

markedly disturbed and developmentally inappropriate social relatedness in most contexts (e.g., the child is avoidant or unresponsive to care when offered by caregivers or is indiscriminately affectionate with strangers);
the disturbance is not accounted for solely by developmental delay and does not meet the criteria for pervasive developmental disorder;
onset before five years of age (there is no age specified before five years of age at which RAD cannot be diagnosed);
a history of significant neglect;
an implicit lack of identifiable, preferred attachment figure.ICD-10 states in relation to the inhibited form only that the syndrome probably occurs as a direct result of severe parental neglect, abuse, or serious mishandling. DSM states in relation to both forms there must be a history of "pathogenic care" defined as persistent disregard of the childs basic emotional or physical needs or repeated changes in primary caregiver that prevents the formation of a discriminatory or selective attachment that is presumed to account for the disorder. For this reason, part of the diagnosis is the childs history of care rather than observation of symptoms. In DSM-IV-TR the inhibited form is described as persistent failure to initiate or respond in a developmentally appropriate fashion to most social interactions, as manifest by excessively inhibited, hypervigilant, or highly ambivalent and contradictory responses (e.g., the child may respond to caregivers with a mixture of approach, avoidance, and resistance to comforting or may exhibit "frozen watchfulness", hypervigilance while keeping an impassive and still demeanour).
It was noted that the diagnosis of RAD ameliorated with better care but symptoms of post traumatic stress disorder and signs of disorganized attachment came and went as the infants progressed through multiple placement changes. At age three, some lasting relationship disturbance was evident. In the follow-up case study when the twins were aged three and eight years, the lack of longitudinal research on maltreated as opposed to institutionalized children was again highlighted. The girls symptoms of disorganized attachment had developed into controlling behaviors—a well-documented outcome. The boy still exhibited self-endangering behaviors, not within RAD criteria but possibly within "secure base distortion", (where the child has a preferred familiar caregiver, but the relationship is such that the child cannot use the adult for safety while gradually exploring the environment). At age eight the children were assessed with a variety of measures including those designed to access representational systems, or the childs "internal working models". The twins symptoms were indicative of different trajectories. The girl showed externalizing symptoms (particularly deceit), contradictory reports of current functioning, chaotic personal narratives, struggles with friendships, and emotional disengagement with her caregiver, resulting in a clinical picture described as "quite concerning". The boy still evidenced self-endangering behaviors as well as avoidance in relationships and emotional expression, separation anxiety and impulsivity and attention difficulties. It was apparent that life stressors had impacted each child differently.