The patient, a 36-year-old female, had bilateral breast augmentation with polyacrylamide hydrogel Omnidene injections 3 years ago at an outside hospital, and a coin-sized lump appeared in her left breast six months after the surgery. However, the lump gradually increased in size and the left breast became significantly deformed. The patient came to our hospital, and her general condition was good. She had full breasts bilaterally, with the left side being larger than the right side, and the upper inner quadrant of the left breast was especially prominent, with normal skin color. MRI was given, and the MR report: “Bilateral changes after breast augmentation, the edges of the filling are not well defined, and multiple masses of abnormal signals are seen in the left breast in front of the filling, with equal T1 and long T2 signals, and the signals are not uniform. Post double breast augmentation, left breast swelling is fast, consider occupancy? Infection?” Operated under general anesthesia 3 days after admission, firstly, incision was made with the right areola, tissue was separated to the injection cavity, jelly-like filling was extruded, about 120 ml, and repeatedly rinsed and scratched, some of the hydrogel injections entered the breast tissue, and in addition to cutting the tissue and pinching and extruding the injections, even some of the invaded tissues were cut out. The right side was cleaned up and a negative pressure drainage was placed. In the left breast, an incision was made in the medial areola and the mass was peeled off at the level of the envelope. Due to the size of the tumor, the incision was extended underneath and the length of the incision was about 8 cm, and a mass the size of a baby’s head was completely removed. After confirming the benign nature of the tumor, 120 ml of hydrogel was removed from the opposite side of the patient. After the operation, the patient was treated with routine hemostasis and anti-infection therapy, and was discharged from the hospital one week later. Post-operative pathological examination described that: the tumor tissue had enlarged lobules with scattered ducts and mildly dilated lumen, normal morphology of glandular epithelium, visible myoepithelial cells, lamellar proliferation of interglandular fibers with mild gliosis; no hydrogel was seen in the tumor tissue; the pathological diagnosis was mega-fibroma of breast. Discussion: There have been more reports of complications caused by polyacrylamide hydrogel (“Ingelfahrer” or “Omnidene”) injection for breast augmentation, and the main complications are: 1. Displacement of the injected material. 2.Multiple hard nodules or lumps in the breast with breast deformation and poor hand feeling. 3.Breast pain, aggravated by upper limb activities, caused by hydrogel injection into the pectoralis major muscle, leading to inflammation of the pectoralis major muscle. 4.Infection, formation of multiple abscesses in the pectoralis major muscle, behind the mammary gland and in the mammary gland, or acute mastitis and breast abscess during late pregnancy and breastfeeding. These complications are common in our clinic, and the treatment method is to remove the hydrogel; however, it is rare to see such a huge tumor occurring in combination with breast augmentation after injection, perhaps the patient had tumor before the breast augmentation surgery, but just neglected to check or not checked out before the surgery. Fibroadenoma is related to estrogen stimulation and mostly occurs in young women. After breast augmentation by injection, due to the fullness of the breast, it has a masking effect on the newly occurred tumor; in addition, some patients are ashamed to let people know that they have undergone breast augmentation surgery and avoid breast examination; our suggestion is that injection patients should have regular follow-up and examination. More importantly, before breast augmentation surgery, the patient must be given the necessary examinations to clarify whether the breast is combined with other diseases. There is another situation that should not be ignored, that is, although the patient does not have local physical symptoms, but the psychological pressure is too heavy, worrying about the danger of the injected material to the body and long-time uneasiness, which has affected the normal life. In these patients, we also recommend surgery to remove the foreign body and relieve the physiological and psychological pressure.