There is a hard lump on the left side of the buttock which is painful to press may be gluteal myofasciitis, lipoma, neurofibroma and other diseases, patients should seek medical treatment in time to clarify the cause of the disease. 1. gluteal myofasciitis: aseptic inflammation of gluteal muscle and fascia, strain is the main cause of its attack, the patient will have a hard lump in the buttock with pain, muscle stiffness, and the symptom will be aggravated after the day cools down, the patient needs to pay attention to the rest, and if necessary, carry out the local closed treatment. 2. Lipoma: it can appear in all parts of the body and is a kind of common soft tissue tumor, which occurs in the left buttock and can be manifested as a painful lump, and it can be surgically excised under the guidance of doctor. 3. Neurofibroma: It is a multi-system damage caused by gene mutation and other factors, and the patient will have a coffee-colored hard lump which is painful when pressed all over the body, and it may be accompanied by the pressure symptoms of the surrounding tissues. If you have the above symptoms, please treat it under the guidance of your doctor.