The article discusses dependability issues in Distributed Systems comprising mobile hosts and wireless data communications (Mobile Distributed Systems). By enabling motion and location independence wireless data communications and mobile hosts allow information access that may occur any time and any place. We show that location and time significantly affect the dependability concept of distributed systems. We demonstrate that the traditional dependability concept is not adequate for Mobile Distributed Systems. Therefore, we enhance the dependability concept to be suitable for Mobile Distributed Systems by extending the definitions of availability and reliability. In addition, we introduce a new attribute of dependability called serveability, which addresses the dependability of the service of Mobile Distributed Systems in a way that a nomadic end-user measures it. We also propose a model of Mobile Distributed Systems that helps the designers and programmers of Mobile Distributed Systems to build distributed systems that offer the best obtainable dependability everywhere and at any time.