Context: Robustness relates to the capability of a system to handle internal and external negative situations and disturbances. Robustness testing is the act of subjecting the system under test to such disturbances in a controlled manner. Objective: The objective of this study is to understand how robustness is considered in the development and testing of large-scale telecom systems, to identify the main challenges related to robustness and robustness testing, and to identify potential improvements to the current situation. Method: An exploratory case study of a Swedish telecom company was conducted. Data was collected through inter- views, study of documentation, and participant observation. Results: A number of challenges related to robustness testing was identified. Even though there is a relatively consistent view of robustness within the company, and robustness is considered to be an important quality attribute, there is a lack of explicit focus on robustness in design and requirements analysis. Conclusion: Our conclusion is that the area of robustness test is challenging for large complex systems, where the understanding of how to provoke complex failures and derive a root cause, as well as defining the correct level of robust design in software is not sufficiently explored.