Obesity is defined as an accumulation of excess body fat and is a medical disease in which excess fat has accumulated to such an extent that it has an adverse effect on the general health of the horse. Obesity is recognised as a cause for concern with regards to the health and welfare of companion animals, with one in five horses kept for leisure purposes currently regarded as obese. While obesity is not widely regarded as a welfare issue by the general public, owners have a duty of care to prevent pain and suffering in horses, and evidence suggests that an obese horse is more at risk of developing painful conditions such as laminitis. Recognition of obesity in horses is an inherent problem, with many owners underestimating the body condition and weight of their horse; this being further complicated by the fact that with larger framed horses, or horses that are already overweight, assessing body condition is more difficult. There are a number of ways of assessing body condition, including measuring actual bodyweight, assigning a body condition score and using formulas such as the body mass index. Body condition scoring is regarded as subjective, but is the most practical means by which owners can regularly assess the body condition of their horse. As with many diseases/disorders, the cause of obesity is multifactorial; however, the most common reason for a horse to become obese is overfeeding coupled with a lack of exercise. Obesity can be addressed by client education, and the veterinary nurse can provide advice with regards to weight management programmes. However, these need to be tailored to the individual horse, and owners need to recognise that they are entering into a long-term commitment.