To compare the benefit achieved by concurrent chemoradiotherapy (CRT) and/or accelerated fractionation (AF) vs. radiotherapy (RT) alone with conventional fractionation (CF) for patients with T3-4N0-1M0 nasopharyngeal carcinoma (NPC). All patients were irradiated with the same RT technique to > or =66 Gy at 2 Gy per fraction, conventional five fractions/week in the CF and CF+C (chemotherapy) arms, and accelerated six fractions/week in the AF and AF+C arms. The CF+C and AF+C patients were given the Intergroup 0099 regimen (concurrent cisplatin plus adjuvant cisplatin and 5-fluorouracil). Between 1999 and April 2004, 189 patients were randomly assigned; the trial was terminated early because of slow accrual. The median follow-up was 2.9 years. When compared with the CF arm, significant improvement in failure-free survival (FFS) was achieved by the AF+C arm (94% vs. 70% at 3 years, p = 0.008), but both the AF arm and the CF+C arm were insignificant (p > or = 0.38). Multivariate analyses showed that CRT was a significant factor: hazard ratio (HR) = 0.52 (0.28-0.97), AF per se was insignificant: HR = 0.68 (0.37-1.25); the interaction of CRT by AF was strongly significant (p = 0.006). Both CRT arms had significant increase in acute toxicities (p < 0.005), and the AF+C arm also incurred borderline increase in late toxicities (34% vs. 14% at 3 years, p = 0.05). Preliminary results suggest that concurrent chemoradiotherapy with accelerated fractionation could significantly improve tumor control when compared with conventional RT alone; further confirmation of therapeutic ratio is warranted.