You mean your child has never laughed before? Like ... when you're playing peek-a-boo ... or because of a tickle or a raspberry on the tummy?
Or do you mean finding something funny and laughing without anyone coaxing him/her to laugh?
If it's the first one ... there could be a disability if no joyful emotion is present.
If it's the second ... it really depends on the child. My Kate is 14 months old and she has been laughing with her brothers at anything funny ... like the dog out getting a cup of water being dumped over her head ... stuff like that, for about a month.
When she finds something funny!!! LOL...no really kinda seriously. My son was like this...until he saw the opening for a movie, Ice Age..a rat was playing with some nuts..my son went nuts..giggling and laughing ! it was the cutest thing that I have ever seen. When it is time she will laugh. The only concern that I would have is if she is showing delays in other areas ...speech, hearing, motor skills etc. take care