Henoch-Schönlein purpura (HSP) is a systemic vasculitis involving the small vessels with distinct clinical features. The etiology of HSP is diverse, and viral infection is one of the many predisposing factors. Cytomegalovirus (CMV) infection mostly affects immune-suppressed patients, but rarely patients with normal immunity can also be affected. Authors experienced a case of HSP patient, with underlying small-cell lung cancer (SCLC) with CMV duodenitis. This is a rare case of HSP diagnosed in SCLC patient with predisposing factor of CMV infection.