The objective of this study was to analyze the effect of radiation therapy duration on event-free survival in patients with invasive carcinoma. Three hundred and sixty patients with FIGO stage IB-IIIB carcinoma of the cervix were treated with external radiation and brachytherapy as first line therapy. Median therapy duration was 45 days. Patients were classified according to whether they had rather long therapies, taking 60 days (the 75th percentile) as an arbitrary cutoff. Cumulative incidences of local recurrence, metastasis, and death were estimated. The 5-year event-free survival rate was 59 +/- 3% for the less than 60 days group and 42 +/- 7% for the more than 60 days group (P = 0.003). In terms of univariate hazard ratio (HR), the relative difference between the two groups corresponds to an increase in hazard of any of the three events considered more than the double (HR = 1.756, P = 0.003) for the longer therapy duration group. A multivariate analysis, which included selected prognostic factors, confirmed these results (HR = 1.76, P = 0.017). A short radiation therapy duration is a highly significant prognostic factor associated with longer event-free survival in carcinoma of the cervix.