The work presented in this paper propounds a solution to the problem of controlling the completeness of a set of requirements written in natural language. The work is integrated in LESD project (Linguistic Engineering for Software Development), whose aim is to develop a computer aided system for analysing and reasoning about software requirements. These requirements are intended to fit some quality factors (traceability, completeness, modifiability, consistency, and verifiability). In LESD, the conceptual structure of natural language specifications is represented using a frame-based knowledge base and the checks to ensure completeness are performed over it. These checks are based on meta-requirements that try to ensure structural completeness (internal and external). So our KB contains general knowledge about the domain (aerospace in LESD project), the requirements, and the criteria to control the quality factors. A prototype has been developed in order to test this approach.