We present a rare case of leiomyoma of the urinary bladder that was diagnosed during pregnancy. The case of a 29-year-old woman primigravida at 13 weeks of pregnancy who presented with 6 months history of abdominal swelling which was gradually increasing in size. Computed tomography done revealed a large heterogenous mass(enhancing) with an area of non-enhancing (necrosis) suggestive of malignant ovarian tumor. The histological findings of the surgical specimen confirmed a leiomyoma of the urinary bladder. The clinical presentation, imaging findings, and management of this relatively rare benign tumor are discussed in this case report.