We read with interest the article by Pandit et al. [1] which provided a model to measure surgical operating list performance, expanding on their previous approach, proposing utilisation as a surrogate marker of efficiency [2] by adding the dimension of productivity. Although we agree with most of their conclusions, we feel that the cost and input aspects of efficiency are somewhat neglected in their approach. Despite initially defining efficiency as work output per cost or effort, they then measure efficiency by assessing just utilisation, stating that ‘efficiency specifically refers to the notion of a team utilising its scheduled list duration fully, without over-running or cancellation’. We argue that maximal use of given resources no longer describes operating theatre efficiency adequately. Considering costs incurred has become increasingly important in view of growing budget restraints and the introduction of the payment-by-results tariff system based on nationwide costing data, which has effectively turned operating departments into profit/cost centres. The pressure for theatre departments and indeed individual surgical operating lists to run cost-effectively is likely to increase in the future. This will only be achieved if costs and input consumption are accurately monitored and form the basis of any productivity and efficiency assessment. To this end, activity-based costing methods such as service-line reporting are currently being introduced in NHS hospitals and are likely to find their way into the operating theatre [3]. Economists describe efficiency as producing the maximum amount of output from a given amount of input or alternatively, producing a given output with minimum input quantities, whilst defining productivity as the ratio of an index of output to an index of input usage [4, 5] This underlines that inputs and costs must be central components of any efficiency measure. We acknowledge that assessing input consumption and monitoring costs down to the level of the individual patient or operating list is difficult. Pandit et al. should therefore not be overly criticised for choosing efficiency measures that are more easily attainable than costing data to arrive at their simple formula. However, their solution can only be a useful starting point to explore measures of efficiency. It will need further development to incorporate costs to be meaningful and address current realities of NHS financing.