We report a case of hereditary breast and ovarian cancer(HBOC)in a young adult. A 31-year-old woman consulted at our hospital for a lump on her left breast. Ultrasonography revealed an irregular-shaped mass. A core needle biopsy was performed, and the pathological diagnosis was invasive ductal carcinoma. There were multiple enlarged lymph nodes in the axilla and internal mammary areas but no evidence of metastasis. She underwent mastectomy and axially dissection. The pathological findings from the surgically resected specimens showed scirrhous carcinoma positive for ER and PgR and negative for HER2/neu protein expression. The tumor size was 16 mm, and 3 axillary lymph node metastases were seen. We identified the pathological stage as T1cN3bM0, stage ⅢC. She received chemotherapy, radiotherapy, and endocrine therapy after surgery. At present, 1 year after surgery, the patient is alive without recurrence. With a low age of onset and a family history of ovarian cancer, she was diagnosed with HBOC as a result of breast cancer susceptibility gene(BRCA)genetic testing. In addition to the recommended surveillance, prophylactic surgery will be performed in the future.