A sliding lump on the left side of the neck may be caused by thyroid tumor, lymphadenitis, thyroid nodule, subcutaneous lipoma in the neck and other diseases. 1. Thyroid tumor: the etiology is unknown and may be related to genetic factors, insufficient iodine intake, radiation, or abnormal serum thyroid-stimulating hormone levels, resulting in a lump in the thyroid area of the neck, which can move up and down with swallowing, and have a sense of obstruction during swallowing. 2. Lymphadenitis: When an infection occurs in a certain part of the body, germs will enter into the lymph nodes of the neck along the lymphatic vessels and cause inflammation of the lymph nodes. Clinical manifestations are reddening of the skin on the surface of local lymph nodes, sliding lumps, accompanied by pain. 3. Thyroid nodules: when suffering from thyroiditis diseases such as Hashimoto’s thyroiditis and suppurative thyroiditis, the surrounding lymph nodes will be enlarged due to bacterial infection or inflammation stimulation, and will slide up and down with swallowing. 4. Neck subcutaneous lipoma: obesity, diabetes and trauma can cause accumulation of subcutaneous fat and thus form lipoma, which is common in any part of the body with fat. Clinical manifestation is that there are lumps under the skin, which can slide when pressed and grow slowly without pain. A sliding lump on the left side of the neck may have other causes, and it is recommended to go to the hospital in time to clarify the cause of the disease and follow the doctor’s instructions for treatment.