Abstract Background Equine endocrinopathic laminitis is common and can be associated with an underlying endocrinopathy, such as equine metabolic syndrome (EMS), pituitary pars intermedia dysfunction (PPID), pasture consumption, or any combination of these factors. Objectives The aim of the study was to improve the risk assessment capabilities of clinicians, and to inform management strategies, for acute endocrinopathic laminitis by prospectively examining the phenotypic, hormonal, and clinical characteristics of the disease in a large cohort. Animals Privately owned horses and ponies (n = 301) of any age, sex, or breed diagnosed with laminitis by a veterinarian. A history of laminitis was acceptable. Methods This was a prospective cohort study. Veterinarians provided information on each case via an online questionnaire after informed consent from the animal's owner, and all data were de-identified before analysis. Serum insulin and plasma adrenocorticotrophic hormone concentrations were measured in each case. Results Most cases were recruited in spring (109/301; 36.2%). Concurrent EMS and PPID resulted in higher basal insulin concentrations (49 [21.5-141]; P < .02) than if an animal had a single underlying cause for their laminitis. The insulin concentration was negatively correlated (r2 = −0.38; P < .001) with the animal's height, being higher in ponies (33[10-14]; P < .001) than horses (9.5 [3-25.7]) and was positively correlated (r2 = 0.12; P = .05) with their grade (severity) of laminitis. Conclusions and Clinical Importance Horses and ponies with concurrent endocrinopathies have more marked hyperinsulinemia. Higher basal insulin concentrations were associated with more severe lameness.