BACKGROUND: In the UK, telephone triage in out-of-hours primary care is mostly managed by nurses, whereas GPs perform triage in Denmark. AIM: To describe telephone contacts triaged to face-to-face contacts, GP-assessed relevance, and factors associated with triage to face-to-face contact. DESIGN AND SETTING: A prospective observational study in Danish out-of-hours primary care, conducted from June 2010 to May 2011. METHOD: Information on patients was collected from the electronic patient administration system and GPs completed electronic questionnaires about the contacts. The GPs conducting the face-to-face contacts assessed relevance of the triage to face-to-face contacts. The authors performed binomial regression analyses, calculating relative risk (RR) and 95% confidence intervals. RESULTS: In total, 59.2% of calls ended with a telephone consultation. Factors associated with triage to a face-to-face contact were: patient age >40 years (40-64: RR = 1.13; >64: RR = 1.34), persisting problem for 12-24 hours (RR = 1.15), severe problem (RR = 2.60), potentially severe problem (RR = 5.81), and non-severe problem (RR = 2.23). Face-to-face contacts were assessed as irrelevant for 12.7% of clinic consultations and 11.7% of home visits. A statistically significantly higher risk of irrelevant face-to-face contact was found for a persisting problem of >24 hours (RR = 1.25), contact on weekday nights (RR = 1.25), and contact <2 hours before the patient's own GP's opening time (RR = 1.80). CONCLUSION: Around 12% of all face-to-face consultations in the study are assessed as irrelevant by GP colleagues, suggesting that GP triage is efficient. Knowledge of the factors influencing triage can provide better education for GPs, but future studies are needed to investigate other quality aspects of GP telephone triage.