Metanephric adenoma is a rare benign tumor of the kidney. It is considered to be derived from embryonic renal tissue and to be the benign counterpart of the Wilms tumor. Although its imaging findings and immunohistochemistry are nonspecific, it has a typical microscopic morphology. We describe a case of a 24-year-old primigravida who presented in the 28th week of pregnancy with lower back pain, fever, malaise, and anemia. At renal ultrasonography and magnetic resonance imaging, a hemorrhagic tumor of 10 cm in diameter originating from the right kidney was seen. Based on the imaging findings, the diagnosis of a cystic renal cell carcinoma with recent hemorrhage was suggested, and a radical nephrectomy was performed. Pathologic examination concluded to a metanephric adenoma. The further pregnancy went on well. The karyotype of the tumor was 46,XX,t(1;22)(q22;q13),t(15;16)(q21;p13). To our knowledge, this is the first report on these chromosomal abnormalities in metanephric adenoma.