Childhood disintegrative disorder (CDD), also known as Heller's syndrome and disintegrative psychosis, is a rare condition characterized by late onset of developmental delays—or severe and sudden reversals—in language (receptive and expressive), social engagement, bowel and bladder, play and motor skills. Researchers have not been successful in finding a cause for the disorder. CDD has some similarity to autism and is sometimes considered a low-functioning form of it. In May 2013, CDD, along with other sub-types of PDD (Asperger's syndrome, autism, rett's disorder and PDD-NOS), was fused into a single diagnostic term called "autism spectrum disorder" under the new DSM-5 manual.

CDD was originally described by Austrian educator Theodor Heller (1869–1938) in 1908, 35 years before Leo Kanner and Hans Asperger described autism. Heller had previously used the name dementia infantilis for the syndrome.

An apparent period of fairly normal development is often noted before a regression in skills or a series of regressions in skills. The age at which this regression can occur varies, after three years of normal development is typical. The regression, known as a 'prodrome,' can be so dramatic that the child may be aware of it, and may in its beginning even ask, vocally, what is happening to them. Some children describe or appear to be reacting to hallucinations, but the most obvious symptom is that skills apparently attained are lost.

Many children are already somewhat delayed when the disorder becomes apparent, but these delays are not always obvious in young children. This has been described by many writers as a devastating condition, affecting both the family and the individual's future. As is the case with all pervasive developmental disorder categories, there is considerable controversy about the right treatment for CDD.