The ICRC has been deploying mobile health units (MHUs) in certain operational contexts. MHUs form part of a strategy involving the provision of occasional ambulatory health services. This strategy is often used in order to reach isolated population groups. In view of their intermittent presence in the field, MHUs suffer from intrinsic constraints which must be taken into account before a decision is made as to which services will be provided. This publication presents practical guidelines for setting up the mobile health units to provide this ad-hoc out-patient care. It presents useful lessons learned and best practices and will be of interest to all those responsible for medical programmes.