To understand why general practitioners prescribe antibiotics for some cases of sore throat and to explore the factors that influence their prescribing. Grounded theory interview study. General practice. 40 general practitioners: 25 in the maximum variety sample and 15 in the theoretical sample. General practitioners are uncertain which patients will benefit from antibiotics but prescribe for sicker patients and for patients from socioeconomically deprived backgrounds because of concerns about complications. They are also more likely to prescribe in pressured clinical contexts. Doctors are mostly comfortable with their prescribing decisions and are not prescribing to maintain the doctor-patient relationship. General practitioners have reduced prescribing for sore throat in response to research and policy initiatives. Further interventions to reduce prescribing would need to improve identification of patients at risk of complications and be workable in busy clinical situations.