One of the current dominant strategies proposed for sustainable urban development is densification. While some advocate the very reasonable benefits of density, others emphasize the potential drawbacks. The main goal of this paper is to provide a systematic overview of the claimed benefits of densification in Swedish practice and relate this to the scientific evidence. For the systematic overview, comprehensive plans from 59 Swedish municipalities, covering plans from both highly urbanized areas as well as more rural regions, are included. The results show that in three out of four cases where density or densification is mentioned, no motive is given. For the other quarter, the most often used motivation is related to transport (19%), services (17%) and urban environmental qualities (14%). The least frequent motives used are related to health (8%) and ecology (2%). The motives in comprehensive plans are for the most part pointing to a positive impact of density on sustainable urban development (77%), which is not always supported by the empirical evidence that more often describe a negative correlation. Furthermore, many of the most frequently used motives in comprehensive plans have little scientific support, which puts new questions on the research agenda. © Published under licence by IOP Publishing Ltd.