Changes in serum glucose levels were examined in a female with insulin-independent diabetes who received a gonadotropin-releasing hormone (GnRH) analog treatment for pelvic endometriosis. The mean blood glucose levels were higher on busereline therapy, and higher levels of hemoglobin A1c were noted on busereline therapy (range 6.9-12.5%) versus pre- and post-treatment (range 5.1-5.9%). Hormonal alteration induced by GnRH analog treatment may impair glucose tolerance.