Objective: To study the correlation of inhibitor of differentiation 1 (Id-1) to tumor invasion and metastasis by examining Id-1 expression levels in different stages of cervical carcinogenesis. Methods: Id-1 mRNA and protein expression was detected in total of 171 cervical samples including precancerous and cancerous tissues by quantitative RT-PCR (qRT-PCR) and immunohistochemistry (IHC), respectively. Twenty-five normal cervical tissues were used as a normal control. Correlation between Id-1 positive rates and expression levels to cancer progression and clinicopathologic features was statistically analyzed. Results: A gradual increase of Id-1 protein expression associated with cervical cancer progression was detected (4%, 16%, 50% and 75.9% in normal, low squamous intraepithelial lesion (LSIL), high squamous intraepithelial lesion (HSIL) and cancer tissue, respectively, p < 0.001). A similar trend of Id-1 mRNA expression was also observed (1.3, 3.4 and 10.4 fold higher than normal tissues in LSIL, HSIL and cancer tissue, respectively, p < 0.001). Furthermore, the Id-1 expression level was correlated to tumor grade (p = 0.005), lymph node metastasis (p = 0.001), interstitial invasive (p < 0.001) and tumor size (p < 0.001). These results suggest that high Id-1 expression is associated with tumor growth, invasion and metastasis. Conclusion: Id-1 expression is correlated to progression and aggressive behaviors in cervical cancer, suggesting a tumor-promoting role for Id-1 in progression of this malignancy. Crown Copyright © 2009.