Despite advanced diagnostic procedures in muscle disorders, creatine kinase (CK) activity is still one of the parameters most often investigated in serum. It is used mainly in neuromyology, and helps to differentiate between myogenic and neurogenic processes. Furthermore, it is applied to monitor the course of the disease and treatment results. Occasionally, marked elevated CK activity requires detailed diagnostic work-up, including electrophysiological, histopathological and genetic studies. In some cases, it enables the final diagnosis to be established. However, there is still a group of patients with so-called idiopathic hyper-CKemia and with no evidence of neuromuscular disorder. As little is known about potentially asymptomatic hyper-CK-emia, these patients should be carefully monitored.