The implementation of choice for patients over where and when they are seen by specialists in hospital outpatient clinics has been supported by electronic referral systems in England and the Netherlands. This paper compares the implementation of 'Choose and Book' in England and 'ZorgDomein' in a region of the Netherlands. For England the analysis draws on national data and published studies on 'Choose and Book', national patient surveys, and qualitative data based on general practitioner (GP) focus groups. For the Netherlands the analysis draws on qualitative data collected during observational study as well as survey data among patients, GPs and medical specialists. We find that despite significant differences in the genesis and design of the policy, similar challenges have been faced. The electronic referral systems have forced changes to the process of care at the interface between primary and secondary care and standardisation between practices. Although these changes have the potential to generate improvements and benefits, for example, convenience, certainty and choice for patients and efficiency gains through for example reduced do not attend rates, repeat consultations and duplicative diagnostic tests; they have also generated problems during implementation including GP resistance. Policy ambitions for patient choice may not be realised if the implementation of the booking system is not carefully designed and evaluated.