Ovarian tissue inadvertently excised along with endometriomas was associated with the presence of pericystic fibrosis and serum levels of CA-125, representing the only clinical parameter for predicting follicle loss before surgery. A consecutive series of 91 ovarian endometriotic cysts were studied, and an inverse relationship between serum CA-125 and the thickness of the fibrotic tissue of the endometrioma capsule was demonstrated.