This paper describes a product line use case modeling approach tailored towards organizations developing and maintaining extremely long lived software intensive systems. We refer to the approach as the PLUSS approach, Product Line Use case modeling for Systems and Software engineering . An industrial case study is presented where PLUSS is applied and evaluated in the target domain. Based on the case study data we draw the conclusion that PLUSS performs better than modeling according to the styles and guidelines specified by the IBM-Rational Unified Process (RUP) in the current industrial context.