Although hepatic dysfunction is common in adult-onset Still's disease (AOSD), sometimes it is difficult to differentiate hepatic dysfunction due to AOSD itself from drug-induced hepatic dysfunction. Further, myalgia often occurs in patients with AOSD; however, AOSD patients complicated with myositis are rare. We report a 43-year-old Japanese man with AOSD who developed myositis and hepatic dysfunction which were deteriorated by multiple nonsteroidal antiinflammatory drugs (NSAIDs) and were dramatically ameliorated by a low-dose steroid therapy. A skin biopsy of salmon pink rash which is characteristic for AOSD showed leukocytoclastic vasculitis, and the markers for vasculitis, plasma von Willebrand factor, and vascular endothelial growth factor levels were elevated in this patient, suggesting an association between AOSD and systemic vasculitis.