Use cases are often very powerful and are popular to use when defining functional requirements for a system. UML supports the use of use cases in object-oriented systems development. However it is not always clear for systems developers on how to use use cases. It can be very confusing in knowing what to include or how to structure use cases. In this study a weather station system has been analysed with an object-oriented approach. Some problems occurred on how to structure scenarios and use cases. Problems also arose on what to describe in the use cases. The problems were analysed and assessed in this paper. The paper points out that the need for guidelines is of great importance.