This study investigates the perspective of the owner–manager of a small or medium-sized enterprise (SME) on the importance of mutual understanding with an external accountant. Mutual understanding means that the owner–manager understands what the accountant is saying and feels understood by the accountant. The results, based on 310 completed surveys of Belgian owner–managers, show that owner–managers who have a high level of mutual understanding use the advice of their external accountant more extensively. This is in turn positively linked to the financial health of an SME. Furthermore, several drivers that enable the establishment of a high level of mutual understanding are explored. Owner–managers with a high level of mutual understanding consider their accountant as a strategic partner, experience a high level of proactive behaviour with them, have a higher frequency of formal contact, and perceive informal contact as important. External accountants should consider these opportunities in their client management and training of internal staff. Education of clients and openness also seem very important, as the level of a client's accounting knowledge, the number of accounting topics owner–managers deal with, and transparency towards the accountant are significantly positively related to mutual understanding.