The main purpose of this chapter is to analyze the relationship between internal and external audit and its effect on external audit fees, through a questionnaire addressed to the external auditors of Portugal and Spain. It obtained 131 answers for Portugal and 149 answers for Spain. According to the results, the competencies and characteristics of internal auditors, as well as the type of activities performed by them and the communication between internal and external auditors, have a significant influence on the decision of using the internal audit work. However, the Portuguese external auditors do not consider this influence to be so significant that it affects the number of substantive tests, the quality of external audit, and external audit fees. However, for Spanish auditors using internal audits decreases the planned hours, the number of control and substantive tests, and improves external audit quality, but does not reflect in the fees to be charged to the client.