Numbers of guide dog owners (GDOs) in the United Kingdom reached 4700 by the end of 1998. Despite this growing trend, little is known about the nature of their visual loss. This paper reports the results of a national three-centre investigation into the residual visual functions and ophthalmic conditions of guide dog owners. Random samples of GDOs (Scotland n = 82, England n = 77, and Northern Ireland n = 87) underwent a detailed visual analysis and interview. GDOs had an overall median age of 53 years. Nationally, they make up just 2.4% of the registered blind population. All GDOs were found to have profound loss of visual acuity, contrast sensitivity or visual fields, but only 43% were totally blind. GDOs in Scotland retained higher levels of residual visual function than those in the other two regions. The main causes of visual loss were congenital and early onset degenerative eye disease (retinitis pigmentosa 18%, optic atrophy 10%). Results taken in conjunction with epidemiological registration trends suggest that the past growth in numbers of GDOs is unlikely to be sustainable. Implications for mobility service providers are discussed. It is suggested that increased optometric input and a multidisciplinary approach could assist present and potential guide dog owners.