A peanut-sized lump at the base of the thigh may be related to lymphadenitis, lipoma and boils. 1. Lymphadenitis: this disease may be related to the infection of staphylococcus aureus, hemolytic streptococcus and other pathogens, which can occur in all parts of the body, preferably in the neck, armpits and groin. The main manifestations are pain, enlarged lymph nodes, etc. The lymph nodes are hard in chronic lymph node inflammation. 2. Lipoma: the etiology of this disease is not yet clear, and it is mostly considered to be related to heredity, chronic inflammation and activation of tumor-causing factors. The patient will have one or more lumps in the skin, which are small in size, usually less than 5cm in diameter, and are commonly found in the neck and shoulders and the proximal parts of the limbs. 3. Boils: If the skin at the base of the thigh is invaded by Staphylococcus aureus or localized skin injury, boils may be induced, resulting in the appearance of localized slightly elevated nodules and the rapid development of firm nodules, such as the shape of a pea. There is no single disease that causes a peanut-sized hard lump at the base of the thigh, so patients are advised to go to a regular hospital to get a clear picture of the cause of the disease.