Introduction: Gestational Gigantomastia (GG) is a rare clinical condition, which is characterized by rapid, diffuse enlargement of the breast tissue. Ultrasound remain an effective imaging modality, in evaluating breast lesion in these group of patients. We present a rare case of GG in a 19-year-old, gravida 2 para 1 woman with massive bilateral breasts enlargements and the sonographic findings of this rare condition. Case Report/Description: A 19-year-old woman currently at 26 weeks of gestation, presented to us with history of bilateral breast enlargement and mastalgia for 1 month. She was treated for mastitis but without improvement. Physical examination revealed grossly enlarged bilateral breasts which were tender on palpation. Serum Prolactin Level is elevated at 6509 mIU/L. Ultrasound examination shows bilateral heterogenous fibro-glandular parenchymal echogenicity, with multiple tubular anechoiec structures. Histopathological Examination (HPE) shows bilateral lobular hyperplasia with florid lactational changes. Patient was treated conservatively with pregnancy safe analgesia and will be reviewed post puerperium to determine resolution or progression of symptoms. Discussion/Conclusion: We present a unique case of GG, which is reported to affect roughly 1 in 100,000 pregnancies. The aetiology and pathogenesis of GG remain elusive, but many theories have proposed that excessive production of prolactin or increase prolactin’s receptor sensitivity during pregnancy lead to this condition. Apart from risk of radiation exposure, sensitivity of mammography in pregnant women is decrease due to increased parenchymal density. Knowledge of radiologic-pathologic appearances of GG and other pregnancy related lesions can help clinician in making correct diagnosis.