It used to be believed that asthma went away when one became an adult, but we now know this is a fallacy.  Even while it may appear your asthma is gone, it is still there in hiding. 

There are many theories why asthma may appear to go away with time.  One is as an asthmatic grows older his air passages become larger and are better capable of dealing with asthma triggers.  Another is he learns to avoid his asthma triggers. 

Asthma is a strange disease in that you can go week, months, even years without having asthma symptoms.  But you must never forget that you still have asthma, and that you should continue to see your doctor at least once a year to monitor your asthma so he can adjust your medicine accordingly (if you still have to take it at all).