a-Ku are rare antibodies, which are reported in course of connective tissue diseases. Their prevalence ranges from 0 to 10% , 2%, on average. The main symptoms associated with the presence of a-Ku antibodies include: myositis, arthritis, Raynaud`s phenomenon and skin lesions. The above features are often defined as autoimmune clinical syndrome associated with a-Ku antibodies. In recent years, three cases with the presence of a-Ku antibodies were observed at the Department of Rheumatology and Connective Tissue Diseases. Case 1, a 77-year-old man, with the diagnosis of mixed connective tissue disease according to Raynaud`s phenomenon, myositis, arthritis and presence of a-ribonucleoprotein antibodies. Moreover, secondary Sjögren syndrome (SS) and myasthenia gravis were diagnosed. Case 2, a 56-year-old woman with longstanding history of Raynaud`s phenomenon, sclerodactyly, myositis and arthritis. Based on clinical manifestations and additional tests, systemic sclerosis and myositis were diagnosed. Case 3, a 46-year-old woman with SS diagnosis, long-standing history of Raynaud`s phenomenon, arthralgia and polyneuropathy. Moreover, HCV infection with the presence of cryoglobulin was confirmed. The presence of a-Ku antibodies in high titers was found in all cases. The clinical conditions improved after steroid and immunosuppressive therapy. In conclusion, clinical syndromes with the presence of a-Ku antibodies are associated with a wide range of non-specific symptoms, regarding muscle, joint and skin involvement, in particular. The conditions are more often diagnosed in the elderly; in the majority of cases, they are characterized by mild courses, good response to steroid therapy and good prognosis.