BACKGROUND: The superiority of volumetric staging (VS) over TNM/TNM-grouping system was previously prospectively tested in our head neck cancer population treated with intensity-modulated radiotherapy (IMRT); gross tumor volume (GTV) was the strongest predictor for disease control. Aim of this work was to specifically assess the prognostic value of VS in oropharyngeal cancer (OC). PATIENTS: Between 04/2002 and 12/2011, 277 consecutive OC patients underwent definitive IMRT. Mean/median follow-up was 33/27months (3-113). Three volumetric cut-offs were used (resulting in 4 GTV subgroups: 1-15cc (14%), 16-70cc (62%), 71-130cc (20%), >130cc (4%)). METHODS: Outcome in the OC subgroup was prospectively assessed with VS and compared with that resulting from TNM and AJCC staging. RESULTS: Primary GTV was most reliably predicting local control (p<0.0001), all other outcome parameters were predicted best by the total GTV (p<0.0001). CONCLUSION: This is -to our knowledge- the first volumetric staging system for OC, and was found to be most reliable in predicting outcome in OC patients treated with IMRT.