—The rise of agile software development methods has led to the abandonment of many traditional practices especially in requirements engineering (RE). Agile RE is still a relatively new research area and the growing use of agile methods in large projects is forcing companies to look for more formal practices for RE. This paper describes experiences gained from a case study of a large agile project. The goal of this case study was to explore how prototyping can solve the challenges of agile RE. Our findings indicate that while prototyping can help with some challenges of agile RE such as lack of documentation, motivation for RE work and poor quality communication, it also needs complementary practices to reach its full potential. These practices include reviewing the big picture regularly, keeping track of quality requirements, and using ATDD (Acceptance Test Driven Development).