My son curves his body always to the left when I lift him into the air.....?

I'd recommend asking for a referral to a neurologist. It may be nothing to worry about, but it could also be an early sign of cerebral palsy. I have a friend whose son began clearly favoring one side at that age. He dragged one leg when he crawled, etc. He was almost 3 when he was finally disgnosed with cerebral palsy. I know it sounds scary, but sometimes cerebral palsy is quite mild, and physical therapy at a young age can make a tremendous difference. Again, it may not be a problem at all - but if it is, the sooner you get professional help, the better.

If you're in the U.S., you can also request an Early Intervention evaluation. It's free, and they measure the child's development in terms of gross motor skills, fine motor skills, verbal skills, etc. Favoring one side might not be a specific item on their assessment list, but you could ask for a physical therapist or occupational therapist to be on the assessment team, and that person would be able to tell you if they thought it was something to be concerned about. Your pediatrician should have the number of the local Early Intervention organization, or you can find it in the phone book.

My daughter is almost 8 months old and is also showing some of the signs of mild cerebral palsy, including high muscle tone. I kept asking our pediatrician about unusual things she was doing, and the pediatrician was really nice but kept saying it was nothing to worry about. When our daughter was referred to a neurologist for other reasons, he picked up on the high muscle tone immediately. Sometimes you really just do need a specialist. If a neurologist examined your son and said it's nothing to worry about, that would be great! And hearing it from a specialist would set your mind at ease. Good luck!