1. In order to investigate the effect of perch width on perching behaviour of laying hens, two experiments in which hens could choose between 7 different perch widths (1 center dot 5, 3 center dot 0, 4 center dot 5, 6 center dot 0, 7 center dot 5, 9 center dot 0 and 10 center dot 5 cm) were conducted. In one experiment (EXP-2P) test cages contained two long perches gradually broadening and narrowing stepwise, in the other experiment (EXP-7P) 7 separate short perches differing in width were placed in the test cages. In each experiment 12 groups of 4 hens were filmed during day and night. The behaviour and location of the hens were recorded and whether the nest box affected hen distribution over the perches was investigated. 2. During daytime, in EXP-2P, there was an increase in perch use with increasing perch width. Hens spent less time on perches of 1 center dot 5 cm wide compared to perches of 9 center dot 0 and 10 center dot 5 cm wide. In EXP-7P, the 1 center dot 5-cm wide perch was also used the least (but only the difference with 4 center dot 5-cm wide perches was statistically significant) but perch use did not increase linearly with perch width. During the night, there were no significant perch width preferences in either experiment. 3. The percentage of active behaviours (preening, walking, drinking, pecking at hen) versus passive behaviours (standing, sitting, sleeping) did not differ significantly according to perch width. 4. In EXP-7P, there was a trend for perch use to decrease with greater distances to the nest box in the morning. 5. A perch width of 1 center dot 5 cm is not recommended for laying hens. For wider perch widths, results were equivocal: they tend to support rather than challenge the widespread use of 4 center dot 5-cm wide perches in commercial units.