Introduction Myopathy of the gracilis or semitendinosus muscles or both has been reported as a cause of hindlimb lameness in dogs. Fibrosis of the gracilis or semitendinosus muscle results in a contracture which produces a distinctive lameness. A review of literature reveals that gracilis-semitendinosus myopathy has been reported in 68 dogs (VAUGHAN, 1979; MOORE et al., 1981; THOREN, 1981; GOBEL et al., 1988; CLARKE, 1989; CAPELLO et al., 1993; LEWIS et al., 1997; KRAMER, 1999), 57 of them being German shepherds. The gracilis muscle was affected in 86 % of the dogs, the semitendinosus in 14 %. The etiology of fibrotic myopathy is unknown. While transection, partial excision, or complete resection of the involved muscle results in immediate resolution of lameness postoperatively, lameness recurred within several months in all dogs with adequate follow-up evaluation reports. The purpose of this case report is to describe the clinical features and the diagnostic method with magnetic resonance imaging as the first report in the veterinary medicine and sonography of a fibrotic gracilis myopathy. Further, a conservative treatment with the clinical outcome follow-up is described. Case report A 4.5 year old female German shepherd dog was presented with a left hindlimb lameness. The hind-limb gait abnormality was characterized by a shortened stride with a rapid, elastic medial rotation of the paw, external rotation of the hock, and internal rotation of the stifle during the mid-to-late swing phase of the stride. On physical examination in the caudomedial stifle region, the distal myotendinous portion of the gracilis muscle was firm and enlarged on palpation. The extension of the left stifle and hock joints was limited. No pain was elicited. Sonography and magnetic resonance imaging (MRI) were performed to confirm the diagnosis. In the ultrasonographic examination the body of the affected gracilis muscle was less homogeneous with focal hypoechoic areas. In the MRI the affected gracilis muscle was more than one third shorter than the unaffected controlateral gracilis muscle. The distal part of the gracilis muscle was increased in diameter. In the region of the pelvic symphysis there was more tissue with signal characteristics of fat and collagenous tissue replacing the muscle. The insertion tendon of the affected gracilis muscle was twice as large as the insertion tendon of the controlateral gracilis muscle. These findings were consistent with contracture of the gracilis muscle on the left hindlimb. Conservative therapy with shock waves, therapeutic ultrasonography and physical therapy (stretching and massage) was provided. The lameness did not resolve but the dog was more joyful in her daily work as a search-dog. No treadmill inspection was done, this outcome is only based on an owner's pure of view approach. Conclusion Fibrotic gracilis myopathy can be suspected on the basis of the typical gait abnormality and the results of physical examination. The definitive diagnosis of fibrotic gracilis myopathy is based on clinical findings confirmed by ultrasonographic examination and magnetic resonance imaging. The treatment with shock waves, therapeutic ultrasonography and physical therapy like stretching and massage could be an alternative conservative treatment.