My son will be 5 in november. he can't have conversationsbut he can read, spell words, make simple sentences andfollows instructions. what is wrong?

He needs an eval: Your son needs a comprehensive evaluation, i recommend either a board certified child psychiatrist or a developmental pediatrician. There is no real way, we here at healthtap can provide an accurate diagnosis without a careful history and examination. Such an evaluation in my office usually takes two hours.

Child delay: Best to have him evaluated by a board certified child psychiatrist for thorough assessment & referrals as deemed necessary for further eval.

Is he in school?: I agree, he needs a comprehensive evaluation to determine if he has a neurological, neurodevelopmental ( e.g., autistic spectrum or other) or psychiatric disorder. Ask your pediatrician for a referral to a specialist in whom he has confidence. Also, call child find for an evaluation of your son for eligibility for early childhood special education, which he can start asap based on levels of delay.