[header] How to know if you have a baker's cyst [title] Look for swelling in the area behind your knee. [step] This swelling is caused by fluid forming in the cyst, causing the area to become inflamed. The swelling will look like a bulge at the back of the knee and is best seen when you are standing up and your leg is straightened. 
[substeps] You can also tell if your knee is swollen by standing in front of a mirror and comparing it to your other knee. [title] Feel for any tightness behind your knee.