The present invention relates to the preparation of substantially purified anti-EDA1 monoclonal antibodies or isolated monoclonal antibody fragments or antigen binding portions or fragments thereof as well as pharmaceutical compositions containing such antibodies. The antibodies may be used in the treatment of disorders relating to excessive action of EDA1 such as hirsutism, ectopic teeth, hyperhidrosis, breast cancer, dermal eccrine cylindroma or skin disorders such as sebaceous gland hyperplasia, comedones, milia, acne, seborrhea, rosacea, steatoma, and furuncles. The anti-EDA1 antibodies are also useful in immunoassays such as sandwich ELISA.