Autism can be diagnosed in children as young as one year of age, researchers say.
Scientists at the Kennedy Krieger Institute in Maryland, USA, studied the social development of children aged 14 to 36 months and found that half could be diagnosed as autistic at their first birthday.
One-year-olds diagnosed with autism found it difficult to play, communicate and interact socially with adults and other children.
Instead of interacting with toys in the usual way, children with autism would repeatedly pick them up and and drop them.
Children with autism also tended to have a smaller vocabulary of sounds, words and gestures that they use to communicate.
Study author Rebecca Landa said: "The fact that we can identify this at such a young age is extremely exciting, because it gives us an opportunity to diagnose children with autism very early on when intervention may have a great impact on development."
She adds that if parents suspect something is wrong they should talk to a healthcare professional.
Landa aims to develop diagnostic criteria for very young children with autism.
"It is vital to identify children with this and other conditions early. Care provision and policy cannot be adapted if the need is not identified. Also, as a Practice Nurse responsible for administration of childhood immunisations, the information we provide parents with must be evidence based. The controversy over the mmr vaccine will not be dispelled, despite all the current evidence unless it can be clearly demonstrated that autism occurs regardless of any immunisations given" - Name and address supplied
"What is the point of early diagnoses when the help isn't there for older children diagnosed later, my son was diagnosed at two and the help he got was extremely minimal, it's disgraceful in the UK" - Name and address supplied