This report describes 2 unusual morphologic features of leiomyomas in patients who had been treated preoperatively with gonadotropin-releasing hormone (GnRH) agonists. In 1 case there was extensive and widespread infiltration of the leiomyoma by numerous small mature lymphocytes, in keeping with a leiomyoma with massive lymphoid infiltration. In the other leiomyoma there were fibrin and foamy histiocytes within the walls of many arterioles, in keeping with a vasculitis. These 2 features, massive lymphoid infiltration and vasculitis, have rarely been described in association with GnRH agonists. Since GnRH agonists are increasingly being used in the management of uterine leiomyomas, pathologists should be aware of these unusual morphologic features in order to avoid diagnostic confusion.