We evaluated the association between tumor-infiltrating FOXP3+ T cells and clinical outcomes in patients with ocular adnexal lymphoma of mucosa-associated lymphoid tissue type (OAML). Pretreatment formalin-fixed paraffin-embedded tissues from 42 patients with OAML were stained with 236A/E7 anti-FOXP3 murine monoclonal antibody as well as CD3, CD4 and CD8 antibodies. The amount of FOXP3+ T cells was numerically quantified using an image analysis program. Front-line treatments were as follows: combination chemotherapy (n = 25); radiotherapy (n = 9); doxycycline (n = 6); and wait and see (n = 2). Complete response (CR) was observed in 20 (50%) of 40 evaluable patients. Median progression-free survival (PFS) was 50 months. A high number of FOXP3+ T cells (n = 21, ≥ 180/0.58 mm(2)) showed a higher CR rate (33%vs 71%, P = 0.013) and tendency towards prolonged PFS (48 vs 67 months, P = 0.110). In the combination chemotherapy group, a high number of FOXP3+ T cells was significantly associated with a higher CR rate (29%vs 82%, P = 0.008) and prolonged PFS (17 vs 79 months, P = 0.003). A high number of tumor-infiltrating FOXP3+ T cells correlates with a favorable clinical outcome in OAML patients.