The severe equine asthma syndrome is one of the most common respiratory problems in older horses. Although epithelial damage and basement membrane thickening are well-known features of airway remodeling in human asthma, pathological features of the bronchial mucosa and their value in the diagnosis of severe equine asthma syndrome are poorly characterized. Therefore, we wanted to determine if classic histologic features characterizing equine asthma are clinically useful. Thirty horses with severe equine asthma and 10 healthy animals were evaluated. A clinical examination, complete blood count, serum chemistry, endoscopic examination, and bronchoalveolar lavage were performed in all the horses. During the bronchoscopy of each horse, three or more biopsies were obtained from either the right or the left first segmental bronchus. The samples were assessed with respect to the surface epithelium, lamina propria, smooth muscle, glands, type of inflammation, and hyperemia. There was a significant difference (P < .05) in all clinical variables between the control and study groups. The horses included in the study group had a mean clinical score of 5.06, wherein the mean clinical score for the control group was 0.7. Cough, nostril flare, and abdominal lift were the components that had the most significant impact on the clinical score. The statistical analysis revealed no statistically significant differences for any histologic variables in the two groups. A classic histological assessment of an endobronchial biopsy is insufficient to differentiate horses with asthma from healthy horses and appears to be less sensitive than the clinical assessment.