Purpose: To evaluate the long term significance of the squamous cell carcinoma (SCC) antigen (Ag) as a tumor marker in uterine cervix carcinoma. Materials and Methods: The SCC antigen levels of pre-radiotherapy and serial post-radiotherapy serum were analyzed in 48 patients who received radiotherapy with histologically proven primary SCC of the uterine cervix. Results: Pre-radiotherapy SCC Ag level was high ($geq$2 ng/ml) at 79.2$\%$. After the treatment, the SCC Ag level was significantly decreased. The SCC Ag level measured at about 3 months after radiotherapy was high at 23.0$\%$. In further follow up measurements, a rise of the SCC Ag to a high level was well associated with clinical relapse. The specificity of the elevated SCC Ag level in association with recurrent or persistent disease was 100$\%$, and the sensitivity was 85.7$\%$. In 3 of 4 lung metastasis cases, lung lesions were detected in chest PA before elevation of the SCC Ag level. The median lead time of the high SCC Ag level to clinical recurrence was 4 months. Conclusion: SCC Ag was a good tumor marker for monitoring treatment effect in patients with increased pre-treatment levels except in case of early lung metastasis. Elevation of the SCC Ag level after radiotherapy accurately predicted the treatment failure with lead time of 4 months. But, in early lung metastasis cases, the SCC level may be normal temporarily. Thus, chest PA should be checked to evaluate the presence of lung metastasis.