British mammalogists have used two different systems for surveying the common dormouse Muscardinus avellanarius: a modified bird nest box with the entrance facing the tree trunk, and a smaller, cheaper model called a "nest tube". However, only few data comparing different nest box systems are currently available. To determine which system is more efficient, we compared the use of the large (GB-type) and small nest boxes (DE-type, a commercial wooden mouse trap without a door) in three Swiss forest. The presence of Muscardinus, potential competitors, and any evidence of occupation were examined in 60 pairs of nest boxes based on 2,280 nest box checks conducted over 5 years. Mean annual occupation and cumulative numbers of Muscardinus present were both significantly higher for the DE than for the GB boxes (64.6% versus 32.1%, and 149 versus 67 dormice, respectively). In contrast, the annual occupation by competitors including Glis glis, Apodemus spp. and hole-nesting birds was significantly higher in the GB than in the DE boxes in all forest (19-68% versus 0-16%, depending on the species and forest). These results suggest that smaller nest boxes are preferred by the common dormouse and are rarely occupied by competitors. These boxes hence appear to be preferable for studying Muscardinus populations.