Distinctive facial features associated with idic(15) - where present at all - are usually very subtle but may include epicanthal folds (skin folds at the inner corners of one or both eyes), downward slanting palpebral fissures, broad forehead, a flattened nasal bridge, button nose, and a high arched palate (roof of the mouth).

Some individuals show other signs that can often be associated with chromosomal conditions, such as pectus excavatum, or a unilateral or bilateral single transverse palmar crease.

Many individuals with idic(15) display features of autism, such as problems with communication and social interactions, obsessional interests (often with interactive mechanisms like wheels, doors or switches), unpredictable sleep cycles (and a reduced need for sleep), and repetitive and stereotyped behaviors (e.g., lining up toys, playing with a toy in the same manner over and over again, hand flapping, rocking back and forth).

However, if they are large enough to contain a number of important genes, they may result in "idic(15) syndrome" which is characterized by learning disabilities, autism and other neurological symptoms.

FISH (Fluorescent in situ hybridization) is used to confirm the diagnosis by distinguishing idic(15) from other supernumerary marker chromosomes.

Array CGH can be used to determine the gene content and magnitude of copy number variation so that the clinical picture can be foreseen.

[citation needed] In general, idic(15) occurs de novo but the parents must be karyotyped to make sure it is not inherited, mostly because this will affect the course of genetic counseling given to the family.

[9] At the present time, there is no specific treatment that can undo any chromosomal abnormality, nor the genetic pattern seen in people with idic(15).

The extra chromosomal material in those affected was present at or shortly after conception, and its effects on brain development began taking place long before the child was born.

Physical, occupational, and speech therapies along with special education techniques can stimulate children with idic(15) to develop to their full potential.

[14] Thus, these should be used with caution and any new medication should be instituted in a controlled setting, with slow titration of levels and with a clear endpoint as to what the expected outcome for treatment is.

Incidence at birth appears to be 1 in 30,000[16] with a sex ratio of almost 1:1; however, since dysmorphic features are absent or subtle and major malformations are rare, chromosome analysis may not be thought to be indicated, and some individuals, particularly in the older age groups, probably remain undiagnosed.

[6] Patients with idic(15) and int dup(15) often feature a distinctive electroencephalography (EEG) signature or biomarker in the form of high amplitude spontaneous beta frequency (12–30 Hz) oscillations.