B7-H1 is a member of the B7 family that inhibits the function of T-cells through its receptor programmed death-1 (PD-1). We examined B7-H1 expression in anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL) and found that it was constitutively expressed in both clinical samples and cell lines. In anaplastic lymphoma kinase-positive (ALK(+)) ALCL cells, B7-H1 expression was suppressed by the blocking of extracellular signal-regulated kinase (ERK) signaling and upregulated by the augmentation of ERK activity by phorbol 13-myristate 12-acetate stimulation, suggesting that B7-H1 expression is regulated by ERK signaling pathway in ALCL. ERK is one of the downstream mediators of nucleophosmin (NPM)/ALK signaling in ALK(+)ALCL, and pharmacological inhibition of ALK was shown to dephosphorylate ERK and down-regulate B7-H1. The involvement of NPM/ALK in B7-H1 expression was also demonstrated by introducing the construct into human non-ALCL lymphoid cell lines, which resulted in B7-H1 expression. In the case of HL, B7-H1 expression was shown to be dependent on the ERK and p38 mitogen-activated protein kinase (MAPK) signaling pathways. These results suggest that B7-H1 expression is controlled by common ERK signaling pathways in ALCL and HL cells. Our findings provide a potentially effective immunotherapeutic strategy for these B7-H1-expressing tumors.