This phase II trial of transoral surgery (TOS) with deintensified postoperative management in human papillomavirus (HPV)-associated oropharynx cancer (OPC) enrolled patients with resectable cT1-2 stage III/IV American Joint Committee on Cancer (AJCC) seventh edition p16+ OPC without matted neck nodes. Those with clear margins, 0-1 + nodes (LN), and no extranodal extension (ENE) were observed (arm A); those with clear margins, 2-4 + LN, or ENE ≤1 mm were randomly assigned to 50 Gy (arm B) or 60 Gy (arm C); and those with involved margins, >4 + LN, or >1 mm ENE received weekly cisplatin and 60-66 Gy (arm D). Among 359 evaluable patients, the 54-month progression-free (PFS) and overall survival (OS) were 90.6% (90% CI, 87.2% to 93.1%) and 95.3% (93.0% to 96.9%), respectively. The 54-month PFS by arm was A 93.2% (79.6% to 97.8%; all four recurrences among N1 patients), B 94.9% (89.7% to 97.5%), C 90.2% (82.7% to 94.6%), and D 85.5% (77.5% to 90.8%). The 54-month OS by arm was A 97.1% (85.7% to 99.4%), B 97.9% (93.5% to 99.3%), C 95.1% (90.1% to 97.6%), and D 92.5% (86.9% to 95.7%). PFS or OS did not differ by primary site or smoking history. TOS and neck dissection with deintensified postoperative management results in outstanding 54-month PFS and OS. Among patients with favorable pathologic characteristics, those with N1 disease are at risk of late recurrence without radiation.