BACKGROUND/AIM: The delayed initiation of treatment is not associated with good clinical outcomes in patients with malignancies. However, few previous studies have examined prognostic factors, including the delayed initiation of treatment, in malignant bone tumors. PATIENTS AND METHODS: One hundred and one patients with malignant bone tumors were enrolled. Univariate and multivariate analyses were performed to identify factors predicting metastasis, including factors that delay the initiation of treatment. RESULTS: The multivariate analysis revealed that high-grade bone malignancy (p<0.01), a >30-day delay in referral to a specialized hospital by a general practitioner (p=0.03), and large tumor size (>77 mm) (p=0.04), were independently associated with metastasis of malignant bone tumors. CONCLUSION: When general practitioners notice a patient with a >77 mm bone tumor, early referral to a specialized hospital within one month might be essential for preventing metastasis.