The last decades’ considerable advances of the psychiatric assessment in People with Intellectual Disability (PwID) do not include the ability to identify Behavioural Equivalents (BE) of psychiatric symptoms and their relationship with different psychiatric syndromes. Recent reports have found BE to be differentially associated with one or more specific Psychiatric Disorders (PD).

The present study was aimed at evaluating the correlations between BE and DSM-5 syndromic groups of symptoms, in a wide multicentric sample of PwID.

An observational cross-sectional analysis was performed for a sample of 843 adults with ID, randomly or consecutively recruited among those living in residential facilities of the National Healthcare System, or in private institutes of care, or those attending psychiatric outpatient clinics. The total sample was administered with the SPAID-G (Psychiatric Instrument for Intellectual Disabled Adult - General version), which is a checklist for the detection of significant behavioural changes from the baseline. The items of the checklist represents BE of the symptoms of the main psychiatric disorders included in the DSM-5.

Many significant correlations were found, some of the most relevant were for mood disorders. Psychomotor agitation, aggressivity, disorganised behaviour and distractibility were most pronounced in bipolar patients; for depressed patients, irritability and weight loss had higher correlations than in other diagnostic groups.

Although not diagnostically specific, some BE seem to be more strongly related with specific PD. This line of research could improve the definition of the specific expression and clustering of psychiatric symptoms in PwID.