The undisturbed roosting behaviour and the reaction of commercial laying hens when roosting on perches was thwarted were studied. Hens were kept in two groups of 26 in litter pens with perches at heights of 23, 43, and 63 cm. Immediately after lights-out and within ten minutes, over 90 % of hens were on perches provided and roosting close together (experiment 1). In experiment 2, hens were kept in groups of three in experimental pens equipped with perches. The birds were tested in four different situations: (1) the pen unchanged (Base), (2) the perch was covered with plexiglass, (3) the perch was removed, and (4) the unchanged pen (Post; control treatment). All birds experienced the four treatments. When perching was not possible, the hens spent less time sitting and tended to spend more time standing than the control hens. The hens also moved more when the perch was inaccessible. When the perch was visible but inaccessible, the birds showed more attempts to take off. The authors interpreted the findings to mean that the birds were experiencing increased frustration and/or exploration, probably to find an alternative roosting site. These results and the findings that there was a high use of perches for night-time roosting under undisturbed conditions led the authors to conclude that laying hens were motivated to perch. They also concluded that hens kept under conditions where perching is not possible may cause the birds to experience reduced welfare.