Why is one side of buttocks so black and blue and other side very little bruising after Brazilian Butt Lift?

Only your surgeon can provide you with the answer you are asking for. None of us have enough information about your situation such as when the surgery was, how much fat was taken out, how much put in, what technique was used, what was the mixture of tumescent fluid, etc. You get the idea. You are best speaking to your surgeon on the phone or in person. We expect our patients to have many questions and we welcome the discussion - it is the post-op care that you deserve, and part of what you paid for. Good luck

Soem bruising can develop, Why one side has more than the other is difficult to predict, but if the buttock is enlarged compared to the other side and more painful, you may want to be evaluated by your surgeon to rule out a hematoma.