Lisa, we thought the same thing about our son, who was always sick from about 9 months of age until about 3.  I discussed that with the Endo many times and she always said emphatically that it had nothing to do with CAH or the Cortef. However, during this timeframe, he was usually undersurpressed due to the liquid cortef problems.  I don't know if his immune system is much stronger now, or if it is because he is under good control with Cortef tabs, but he has rarely gotten sick in the last 9 months.  (knock wood)  Is your child undersurpressed (what is OH-17P level)? 

Andy