A welfare assessment was conducted during 475 observations of 75 long-line tethered horses and 587 observations of 112 freerange horses kept on public grazing land in South Wales over a six-month period from March to August 2010. The observations included quantitative and qualitative behavioural assessments, assessments of physical welfare and assessments of the environment of the horse. Multi-level modelling was used to identify the significant factors affecting each measure. Tethered horses had similar behavioural repertoires to free-range horses but there were differences related to tethering, such as fewer observations of walking, trotting and cantering, increased vocalisations occurring during the observation and poorer qualitative ‘mood’ scores. There were few observations of severe physical welfare problems in either tethered or free-range horses, however tethered horses were observed more often to have eye abnormalities, hoof cracks, lameness and signs of limb pain but less often with mane and tail tangles, as thin or as dirty. Shelter from wind, rain or sun was available to almost all free-range horses (99.8% of observations) but was only found during 16.5% or fewer observations of tethered horses, giving them a greater risk of poor welfare during inclement weather. Similarly, tethered horses were infrequently observed to have access to clean water, and their willingness to drink when offered water, suggests the provision of water was inadequate and tethered horses may have been thirsty. There were significant confounding effects of the observer or climatic factors for some behavioural and physical measures that should be considered when conducting future studies.