Since the introduction of "Payment by Results", departmental income has been linked to clinical activity, and the coding of theatre activity (Office of Population, Censuses and Surveys Classification of Surgical Operations and Procedures (4th revision), OPCS-4) must be accurate and timely. We assess the accuracy of OPCS-4 coding for patients having microvascular free tissue transfer for head and neck cancer, and evaluate the impact it has on departmental income. Codes for a consecutive cohort of patients were checked to identify inaccuracies and the tariffs were recalculated. Incorrect coding in 11/21 cases resulted in a financial loss of £77449.00 because reconstruction had not been recorded as F39.1, which would automatically place it in the maximum income group, CZ04. If funding is to be optimised surgeons must be cognisant of the importance to code procedures accurately with respect to financial reimbursement. Regular monitoring of coding is suggested, including that of coexisting morbidities.