Mobile ad hoc networks (MANETs) are infrastructureless networks formed by wireless mobile devices with limited battery life. In MANETs for civilian applications, the network nodes may not belong to a single authority and they may not have a common goal. These MANETs are particularly vulnerable to selfish behavior, as some nodes may prefer saving resources to forward data. There are a few generic reputation-based systems for MANETs which could be used to enforce cooperation among nodes. However, we envision that the system performance can be highly improved by using cross-layer techniques that take into account the specific characteristics of each particular service. In this article, we propose a distributed and easy-to-implement routing mechanism based on reputation for the provision of MPEG-2 video-streaming services over MANETs. The main novelty that we introduce regarding the existent literature is that our proposal is service aware, that is to say, we consider the video-streaming service characteristics to develop a cross-layer design with the routing protocol. In addition, we do not introduce extra signaling overhead to monitor reputation because we use the standard video-streaming end-to-end signaling. Finally, simulation results show that our proposal clearly outperforms both standard Dynamic Source Routing (DSR) and OCEAN (a generic reputation-based mechanism).