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.
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.
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.