Wilson disease (WD) is an autosomal-recessive disorder of hepatic copper metabolism that has tremendous variability in its presentation. Phenotypic diversity of the disease can lead to delayed diagnosis. We describe a case of WD in a 10-year-old boy presenting with 3 months of increasingly intense, spasmodic lower extremity muscle cramps. Physical examination revealed tenderness on calf palpation and dark flat lesions over his ankles, knees, and elbows. Initial testing revealed creatine kinase of 302 IU/L (normal 24-248 IU/L), hemoglobin of 8.9 g/dL (11.5-15.5 g/dL), aspartate aminotransferase of 114 IU/L (16-52 IU/L), alanine aminotransferase of 54 IU/L (2-30 IU/L), and myoglobinuria. Extensive evaluation of his myopathy, including MRI and muscle biopsy, was negative. Additional laboratory tests revealed a prothrombin time of 21.3 seconds (11.8-15.5 seconds), total bilirubin of 1.4 mg/dL (<1 mg/dL), direct bilirubin of 0.5 mg/dL (<0.3 mg/dL), albumin of 2.1 g/dL (3.1-4.6 g/dL), a reticulocyte percentage of 4.5% (0.5%-2.5%), a negative Coombs direct antibody test, ceruloplasmin of 3 mg/dL (21-51 mg/dL), and 24-h urine copper of 393 mug/24 h (15-60 mug/24 h). Liver biopsy showed patchy advanced fibrosis, mild inflammation, positive staining for copper, and a tissue copper concentration of 768 microg/g (10-35 mug/g). Brain MRI revealed symmetric intrinsic T1 shortening within bilateral basal ganglia. Trientene therapy was initiated for WD. Symptoms and laboratory abnormalities resolved and remain normal at 21 months' follow-up. Musculoskeletal involvement in WD is uncommon and typically defined as bone demineralization, arthropathy, or hypokalemic muscle weakness. In patients with unexplained musculoskeletal symptoms and hepatic abnormalities, a diagnosis of WD should be considered and appropriate evaluation initiated.