Here is what my doctor said I have. I don't advise self-diagnosis, so be leary (sorry about the formatting:

Patellofemoral pain syndrome

Patellofemoral pain syndrome is a condition that causes pain in the ******************front of the knee. It frequently occurs in teenagers, manual laborers, and ******************athletes. It sometimes is caused by changes in the cartilage under the kneecap, ******************such as a wearing down, roughening, or softening of the cartilage.

Patellofemoral pain syndrome may be caused by overuse, injury, ******************excess weight, or a kneecap that is not properly aligned (patellar tracking ******************disorder).

Symptoms include:
Pain, especially when sitting with bent knees, *************************squatting, jumping, or climbing stairs.
Occasional knee buckling, *************************where the knee suddenly and unexpectedly gives way and does not support body *************************weight. This might occur because of pain, muscle weakness, or a torn *************************ligament.
A catching, popping, or grinding sensation with walking *************************or knee movement.

Patellofemoral pain syndrome can be relieved by avoiding activities ******************that make symptoms worse.
Avoid sitting or kneeling in the bent-knee *************************position for long periods.
Adjust a bicycle or exercise bike so *************************that the resistance is not too great and the seat is at an appropriate height. *************************The rider should be able to spin the pedals of an exercise bike without *************************shifting weight from side to side, and the legs should not be fully extended at *************************the lowest part of the pedal stroke.
Avoid bent-knee exercises, *************************such as squats, deep knee bends, or 90-degree leg extensions.

Other methods to relieve pain include:
Nonprescription anti-inflammatory medication *************************(NSAIDs), such as ibuprofen or naproxen sodium, to decrease swelling, *************************stiffness, and pain.
Ice and rest.
Physical therapy *************************exercises, such as stretching and straight-leg raises, to strengthen the *************************quadriceps muscle.
Taping or using a brace to stabilize the *************************kneecap.
Surgery.