Purpose: The effects of estrogen only on prostate tissue were studied in 9 aging male transsexuals who had undergone orchiectomy. Materials and Methods: Prostate volume was measured by ultrasound. Biopsies were stained for prostatic acid phosphatase (PAP), prostate specific antigen (PSA), Ki-67 and sex steroid receptors. Results: Prostates were small, and biopsies showed PAP and PSA in most cases. No malignancy was found. Few androgen receptors were detectable but there were ample estrogen and progesterone receptors in stroma and epithelium. Conclusions: Prostates were small after long-term estrogens only. The sex steroid receptor content was considerably changed. PSA and PAP in the specimens suggested that their production does not depend on testicular androgens alone.