A unique case of prostatic stromal sarcoma (PSS) that recurred in the pelvic cavity with massive high‐grade prostatic intraepithelial neoplasia is described. A 52‐year‐old man who presented with urinary retention underwent a radical cystoprostatectomy. Tumour tissues of the prostate showed an admixture of hyperplastic glands and markedly cellular stroma of spindle cells arranged in a fascicular pattern, and the tumour was diagnosed as PSS. 66 months after the operation, CT scans revealed three recurrent tumours around the bilateral obturator and left fore iliopsoas. The recurrent tumours were biphasic neoplasms, as before, but the epithelial component had grown prominent and manifested overt atypia in a manner resembling high‐grade prostatic intraepithelial neoplasia. Our findings suggest that not only the stromal component but also and the epithelial components of PSS may have malignant potential.