Adenopathy is very common and can occur because of something as mild as having a sore throat to a more serious condition, like cancer. Cancerous nodes are often hard and affixed to the surrounding tissues, and are not usually painful. Benign nodes, such as those from infections, are usually painful.
When lymph nodes are persistently swollen and/or become larger, you should seek medical attention. If you are already under the care of a physician, make sure your doctor is aware if your lymph nodes are swollen.