Medical records of 23 dogs with unilateral and 3 dogs with bilateral chronic bicipital tenosynovitis were reviewed. Mean age of affected dogs was 4.6 years (SD, 2.0 years), and mean body weight was 32.6 kg (SD, 14.5 kg). Neither a breed nor a gender predilection was detected. All dogs had a history of intermittent or progressive weight-bearing lameness that became worse after exercise. Mean duration of lameness prior to medical or surgical treatment was 6.5 months (range, 0.25 to 24 months). In all dogs, signs of pain were evident during palpation of the biceps tendon within the intertubercular groove. Radiography revealed sclerosis or osteophytosis of the intertubercular groove in all 29 shoulder joints. Mild degenerative joint disease was evident radiographically in 17. Arthrography was performed in 12 joints, and in 11 there were irregularities of or filling defects along the biceps tendon. Arthrocentesis was performed on 17 joints; 14 synovial fluid samples had cytologic abnormalities consistent with degenerative joint disease. Medical treatment, consisting of injection of methylprednisolone acetate into the biceps tendon and its synovial sheath, was attempted in 21 of the 29 affected shoulder joints. Surgery, which consisted of tenodesis of the biceps tendon, was attempted in 14 joints; 8 of these had not been treated medically; the remaining 6 had poor results following medical treatment. Gross and histologic findings consistent with chronic bicipital tenosynovitis were observed in all 14 joints in which surgery was performed. Seventeen of the medically treated shoulders were available for clinical evaluation, and results were excellent or good in 7.(ABSTRACT TRUNCATED AT 250 WORDS)