1. ISA Brown hens were housed as groups of 4 from 18 to 72 weeks in 24 cages 450 mm deep, each with a softwood perch of rectangular cross-section fitted across the rear. There were 4 treatments, each with 6 cages: cage widths and perch lengths were 480, 520, 560 or 600 mm. 2. Daytime perching did not differ significantly between the treatments. At night, over the whole year, 81% of birds in the 480 mm cages and 86% in the 520 mm cages roosted on the perch. This figure reached about 95% in the 560 and 600 mm cages, significantly more at most ages than in the 480 mm cages. 3. Feather damage was slightly less, but claw problems slightly more, in the 2 wider treatments than in the 2 narrower treatments. Birds in the wider cages were calmer when approached or handled by humans than those in the narrower cages. This may have been associated with variation in space allowance between the treatments. 4. There was a trend for lower production in the 480 mm cages than in the other treatments which may have been associated with the reduced feeding space in this treatment. There were few other treatment differences in production traits. 5. The balance of the evidence from this study is that when perches are provided in laying cages for medium weight hybrids, 140 mm of perch space per hen is adequate. For the amelioration of a number of the welfare problems of conventional cages, provision of perches should be combined with other modifications.