Normal and diseased superficial digital flexor tendons at different stages of healing from seven Thoroughbred horses, aged 3–6 years, were evaluated by correlation of gray scale histogram analysis of tendon cross‐sectional ultrasonograms with histopathologic examination. Normal tendon and tendons at different stages of healing, excluding acute tear stage, were characterized by normally distributed histogram patterns. The histogram mean value of normal tendons was higher than the corresponding values in diseased tendons at different stages of healing (p < 0.01). In addition, the histogram mean of acute lesions was lower than for early fibrosis or healed lesions (p < 0.01). The histogram mean increased as healing progressed. The results show that gray scale histogram analysis of tendon ultrasonogram can be used to distinguish between normal and abnormal superficial digital flexor tendon in racing horses.