Purpose: Childhood and adolescent survivors of cancerous lower-extremity bone tumors may be at unique risk of uncertainty about their future because of their specific cancer and/or physical disabilities secondary to treatment. This study aimed at clarifying survivors' uncertainty and related factors, including physical functioning, limb pain, and management of affected limbs. Methods: Self-administered questionnaires were distributed at two cancer hospitals in Japan. Thirty-six survivors diagnosed with osteosarcoma or Ewing sarcoma were included in our study. Uncertainty was evaluated by using Mishel's Uncertainty in Illness Scale-Community Form (MUIS-C), and physical functioning was evaluated by using The Toronto Extremity Salvage Score (TESS). Results: The average score of MUIS-C was lower that than reported for other previously studied childhood cancer survivors. Uncertainty was significantly higher in survivors who had lower levels of education, pain in their limbs, and difficulty managing their affected limb. Correlational analyses indicate that high scores for TESS, less limb pain, and high ability to manage affected limbs were related to low uncertainty. Conclusion: Health care providers need to assess survivors' degree of limb pain and their self-management for general health and affected limbs. It might be possible to improve their daily life. Assisting childhood and adolescent survivors of bone tumors to manage affected limbs and limb pain could prevent chronic uncertainty.