Objectives: Clinical manifestations of mitochondrial disorders(MIDs) may be mild at onset and may show wide intra- and interfamilial heterogeneity. Case report: A 56yo male developed myalgias of the external eye muscles two months after intake of fluvastatin, followed by muscle aching of the thighs. Four months later he developed muscle wasting and noted easy fatigability and excertional dyspnea. He presented with sore neck muscles, reduced tendon reflexes, descrete wasting, and fasciculations of the right calve. There was slight leucopenia, reduced folic acid, and a myogenic EMG of the right deltoid muscle. Muscle biopsy revealed increased fiber size variation and scattered COX-negative fibers. Biochemical investigations revealed markedly reduced activity of the NADH-CoQ-oxido-reductase, why a MID due to a complex-I-defect was diagnosed. Conclusions: MIDs due to complex-I-deficiency may start with only mild symptoms, such as myalgia, fatigue, and wasting. Myalgia and fatigue should be considered as manifestation sof a complex-I defect.