When the lymph nodes in the inner thigh, also known as inguinal lymph nodes, become enlarged and painful, the most common cause is a benign infectious disease, such as inflammation of the lower extremities that can cause enlarged lymph nodes in the inner thigh. In addition, inflammatory infections of the vulva and genitalia can also cause enlargement of the inguinal lymph nodes. Less commonly, malignant tumors can cause swollen inguinal lymph nodes. In general, most inguinal lymph node swelling due to tumors is not significantly painful because it usually grows slowly, but in exceptional cases, swollen inguinal lymph nodes can also occur if the tumor is growing rapidly. Once this occurs, you should visit the hospital for appropriate investigations.