Transcription factor Snail1 is a mediator of cell migration and survival, and expression is elevated in several cancer types. The Snail1 gene is reportedly amplified in prostate cancer (PC), and we investigated Snail1 expression in PC. Immunohistochemical Snail1 staining was determined on a tissue microarray which includes 327 specimens of PC, 30 specimens from patients with benign prostatic hyperplasia (BPH), benign tissue from 30 PC patients and 15 high-grade prostate intraepithelial neoplasia (high-grade PIN) specimens. Clinicopathological and follow-up data were available for all patients. No BPH specimen and only 21% of benign tissue from PC patients showed high expression of Snail1. Only 7% of high-grade PIN patients expressed a high level of Snail1. In contrast, approximately 50% of PC tissue from patients with PC showed marked nuclear immunostaining. Snail1 immunostaining was significantly associated with Gleason score (p<0.05). Snail1 expression was not correlated to T stage, metastasis at time of diagnosis, risk of or time to recurrence. Snail1 expression was significantly increased in PC with a positive correlation to dedifferentiation, but not to cancer progression or prognosis. The presented data indicate that Snail1 expression is upregulated from the early stages of PC.