Do multiple café-au-lait spots on my baby's skin mean he has a serious disease?

Maybe . It is best to talk with your doctor if you notice a large number of cafe-au-lait spots. A few may not be a sign of any underlying illness (my daughter has a huge one since birth on her trunk). However, multiple spots may can be a sign of a rare conditoin called "neurofibromatosis". There are other features that are associated with this condition so consult your doctor if you have any concerns.
Possibly. Although it is common for children to have a cafe-au-lait spot or two, more than 5 might be an indication of neurofibromatosis (nf). It is important to remember that cafe-au-lait spots by themselves are not diagnostic of nf. Other criteria are required as well, such as a relative with nf, lisch modules, neurofibromas, etc. Please check with your doctor.
Not necessarily. Multiple "cafe-au-lait" spots on your baby's skin may be simply that - benign spots of pigmentation. It is estimated that about 20% of the population has them. Multiple cafe-au-lait spots can also be associated with some rare disorders, including neurofibromatosis. See dr. Greene's blog article for more: http://bit.Ly/fwszi1 and ask your pediatrician.