Shortage of general practitioners (GPs) and an increased political focus on primary care have enforced the interest in efficiency analysis in the Danish primary care sector. This paper assesses the association between organisational factors of general practices and production and efficiency. We assume that production and efficiency can be modelled using a behavioural production function. We apply the Battese and Coelli (Empir Econ 20:325-332, 1995) estimator to accomplish a decomposition of exogenous variables to determine the production frontier and variables determining the individual GPs distance to this frontier. Two different measures of practice outputs (number of office visits and total production) were applied and the results compared. The results indicate that nurses do not substitute GPs in the production. The production function exhibited constant returns to scale. The mean level of efficiency was between 0.79 and 0.84, and list size was the most important determinant of variation in efficiency levels. Nurses are currently undertaking other tasks than GPs, and larger practices do not lead to increased production per GP. However, a relative increase in list size increased the efficiency. This indicates that organisational changes aiming to increase capacity in general practice should be carefully designed and tested.