Uterine leiomyomas develop from uterine smooth muscle cells, which are known to be regulated by estrogen and other growth factors. The purpose of this study was to investigate the role of expression of parathyroid hormone related-peptide (PTHrP) in the growth of uterine leiomyomas treated or untreated with gonadotropin-releasing hormone agonist (GnRH-a). Thirty-nine leiomyoma tissues were obtained from 36 patients who had been treated with GnRH-a (n=10) or without GnRH-a (n=29). The intensity of PTHrP immunostaining was categorized into three grades; “negative”, “weakly positive”, and “positive”. Leiomyoma cell growth was estimated by the proliferating cell nuclear antigen (PCNA) labeling index (LI) with an image analyser. We also investigated the correlation between PTHrP expression and cell proliferation or histopathological findings. In the GnRH-a-untreated group, LI of the PTHrP “positive” group was significantly higher than that of the PTHrP “negative” group, but the intensity of PTHrP immunostaining did not correlate with LI in the GnRH-a-treated group. PTHrP expression did not correlate with histological findings or clinical parameters (age and phase of menstrual cycle) in either the GnRH-a-treated or the -untreated group. In addition, the expression of mRNA for PTHrP and its receptor was detected in leiomyomas by reverse transcriptase-polymerase chain reaction (RT-PCR). Our results indicate that the expression of PTHrP in leiomyomas correlated positively with cell growth in the GnRH-a-untreated group, suggesting that PTHrP may act as a local cell growth modifier in an autocrine/paracrine fashion on uterine leiomyomas.