PIP: This article reports the case of a bleeding ectopic decidual reaction from the serosal surface of the fallopian tube in the absence of pregnancy in a woman who had received a long-acting injectable contraceptive. This complication has not been previously reported as a possible side-effect of progestogen administration. The patient, a 42-year old Chinese woman, received 3 injections of medroxyprogesterone acetate 150 mg at 3-month intervals and then switched to the combined contraceptive Microgynon (.15 mg levonorgestrel and .03 mg ethinyl estradiol). The 2nd course of Microgynon was completed 1 week before her admission to the hospital with right lower abdominal pain and secondary amenorrhea for 9 months. A hematocele was found on the right side of the pouch of Douglas. Decidual reaction is an exaggeration of the normal response of the endometrium to progesterone. In the absence of pregnancy, ectopic decidual changes have been attributed to the stimulation of appropriate cells by progesterone and progesterone-like substances from the corpus luteum or the adrenal cortex.