There are different types of ovarian cysts. Each has unique causes and characteristics. The size of an ovarian cyst can also vary depending on the type of cyst; the two main types of ovarian cysts are: • Functional Ovarian Cysts: These are the most common type of ovarian cyst and are typically harmless and short-lived. • Pathological Cysts: These cysts grow in the ovaries; they may be benign (harmless) or malignant (cancerous).   Size is one of the factors that determine whether a cyst needs to be removed with surgery. Generally, surgery is not recommended for ovarian cysts unless they are larger than 5 to 6 centimeters (about 2 to 2.4 inches) in size. However, this guideline can vary. For example, a simple cyst may be left alone until it is 10 cm (4 inches) in size, but cancerous cysts may be removed when they are much smaller in order to prevent growth and proliferation.