Gastrocnemius musculotendinopathy is a potential cause of chronic hindlimb lameness in medium to large breed dogs. A history of athletic activity must not necessarily be present. Magnetic resonance imaging shows signal changes and uptake of contrast agent in the region of the origin of the gastrocnemius muscle. A combination of T1 pre- and post-contrast administration and T2 weighted sequences completed by a fat-suppressed sequence in the sagittal plane are well-suited for diagnosis. Conservative treatment generally results in return to normal function.