my ds didn't have any allergies that we knew of, and never had any infections, but his adenoids were so large that they caused him to have constant fluid in his ears that left him deaf(thankfully not permanently). Also, all the sleep issues that others have mentioned, and behavior issues.
We took them out at 4.5 yrs and have never regretted it. The ENT dr also said that his was the biggest he'd seen.
I also think some kids are just naturally enlarged.
tina UC mama of 5!