Abstract Introduction Radiotherapy for oropharyngeal cancer often causes severe side effects. If the primary tumour is localized to the tonsillar region, elective irradiation may be limited to the ipsilateral neck, sparring the contralateral normal tissues. We wanted to study the consequences of volume sparring on all prospectively registered morbidity endpoints. Methods and patients Medical records, treatment charts and database information were collected for all 158 oropharynx cancer patients treated from 1998 to 2002 at Aarhus University Hospital. Of the 139 patients treated with curative intent 40 were treated with an ipsilateral technique. Results Primary tumour extension outside the tonsillar fossa and T-stage were the only patient-, disease- and treatment related factors that differed between ipsilaterally and bilaterally treated patients. Loco-regional control and survival were not negatively influenced by the volume sparring technique. Side effects were reduced, in the ipsilaterally treated group, for all endpoints: xerostomia, dysphagia, hoarseness, atrophy, fibrosis and oedema. The number of patients experiencing moderate to severe toxicity was more than halved with ipsilateral treatment for all endpoints except fibrosis. Conclusion For selected patients with tonsillar cancer without involvement of midline structures, ipsilateral treatment is safe and reduces morbidity compared with bilateral treatment.