Because autistic people are an incredibly diverse group, their communication abilities vary widely. Some autistic people experience a speech delay (or no speech at all), while others may be hyperlexic.
Communication can be a major challenge for autistic children and adults. Some autistic children lose speech at 18-24 months, which is known as "regressive autism." Some develop language late, or not at all.
Some autistic children develop echolalia, repeating words and phrases (usually but not always understanding what they mean). Autistic children are also impaired in their understanding of body language and other non-verbal communication.
Speech development varies from person to person on the spectrum. While some may speak early, some autistic people learn to speak late (e.g. age 5, age 10, or age 15) or find speech impossible. In some rare cases, young children will begin to speak and then lose speech. If this happens, immediately contact a doctor, because sometimes it is caused by anxiety disorders or abuse by healthcare providers.
Still, inability to speak does not mean that autistic people are unaware or unintelligent. Autistic sometimes find communicating much easier over the internet, and can establish a strong presence in chat rooms, blogs, or social networks.
Autistic people may use words in a startling and different way. This can develop into a rare gift for humor. Some are so proficient at written language as to qualify as hyperlexic.
Hyperlexic autistic people may have a highly formal or pedantic way of speaking. A five-year-old child with this condition may regularly speak in language that could easily have come from a university textbook, especially concerning their special area of interest. Less pronounced examples include using advanced vocabulary (e.g. "circumspect") in everyday language.
Autistic children may show advanced abilities for their age in language, reading, mathematics, spatial skills, or music, sometimes into the 'gifted' range. Some other typical behaviors are echolalia, the repetition or echoing of verbal utterances made by another person, and palilalia, the repetition of one's own words. 
A 2003 study investigated the written language of autistic children and youth. They were compared with neurotypical peers in a standardized test of written language skills and legibility of handwriting. In written language skills, no significant differences were found between standardized scores of both groups; however, in handwriting skills, the autistic participants produced significantly fewer legible letters and words than the neurotypical group. Another analysis of written samples of text, found that autistic people produce a similar quantity of text to their neurotypical peers, but have difficulty in producing writing of quality. 
Echolalia and Literal Communication
Echolalia, the repetition of words and phrases, may be used as communication. Autistic people may repeat a phrase in an attempt to communicate something, or convey a feeling that is associated with that phrase. If this is confusing to people, they can ask for clarification.
Literal interpretation is another common, but not universal hallmark of autism. Psychologist Tony Attwood gives the example of a girl with AS who answered the telephone one day and was asked, "Is Paul there?" Although the Paul in question was in the house, he was not in the room with her, so after looking around to ascertain this, she simply said "no" and hung up. The person on the other end had to call back and explain to her that he meant for her to find him and get him to pick up the telephone. Many autistic people can be taught to understand figurative language, such as humor and exaggeration.
Nonspeaking Autistic People
Nonverbal autistic people can still be quite communicative. Some use apps that speak what they type, or they can select specific words from a table to form a message. They may also learn sign language. They can also communicate through body language (e.g. pointing at things) and stimming (e.g. flapping hands when they are happy). While autistic children may not say "I love you" through their words, they may communicate it through hugs, pictures, smiles, or time spent with their loved ones.
Sometimes, during periods of sensory overload, an autistic person may become temporarily unable to speak. This will alleviate after the autistic person has had some quiet time to rest and recharge.
Nonspeaking autistic people can still live happy and productive lives. One prominent example is writer and activist Amy Sequenzia.
Communicating with Neurotypicals
Since non-autistic people are often unfamiliar with the autistic body language, autistic people often struggle to let other people know what they need. As anybody might do in such a situation, they may cry in frustration or resort to grabbing what they want. While waiting for neurotypical people to learn to communicate with them, autistic do whatever they can to get through to them.
Communication difficulties may contribute to autistic people becoming socially anxious or depressed or prone to self-injurious behaviors. An alarmingly high number of autistic people are being diagnosed with co-morbid mood, anxiety and compulsive disorders which may also contribute to behavioral and everyday life challenges.
Neurotypical people can help by being patient and asking questions to clarify if the message isn't getting across well.
- Bauer S. Asperger Syndrome. The Source (2000).
- Attwood (1998), p. 109.
- Myles BS, Huggins A, et al. Written language profile of children and youth with Asperger syndrome: From research to practice. Education and Training in Developmental Disabilities. 38: December 4, 2003, 362-369. Abstract.
- Cynthia Kim: Echolalia - That's What She Said
- Real Social Skills: When Repetition is Communication
- Dr. Tony Attwood, Asperger's Syndrome: A Guide for Parents and Professionals (1998), p. 78.
- wikiHow: How to Teach Figurative Language to Autistic People