In the debate on sustainable energy use, one important aspect tends to be systematically overlooked. Sustainability may be increased by developing technological innovations and measures to promote energy conservation, but so-called rebound effects constitute a potential and largely underestimated impediment towards the accomplishment of the intended goals. In short, these rebound or take back effects involve the spending of monetary savings from energy conservation on activities or the acquisition of goods that, in their turn, will enhance energy use or environmental pollution. Such activities or purchases (e.g. taking longer showers, adding more lighting to the garden, buying a dryer or a waterbed, or booking an additional holiday flight) might reduce or even cancel out the beneficial effects that were intended in the first place. Partly because these effects seem to be neglected in most research on sustainable energy use, it is difficult to estimate their size and impact. This paper provides insight into the results of an exploratory study of energy related behavior and energy related purchases indicating rebound effects in Dutch energy efficient dwellings. It is concluded that there is a likely presence of rebound effects in both these respects. The discussion entails suggestions for counteracting rebound effects together with recommendations to highlight this phenomenon in future research.