PURPOSE: To review the clinical, radiological, and histopathologic features in 8 patients with natural killer/T-cell lymphoma (NKTL) involving the orbit and/or ocular adnexa, and to describe the responses of these patients to various treatment regimens. Design: Retrospective observational case series. Participants: Eight patients (5 male, 3 female) with NKTL involving the orbit and/or ocular adnexa were identified from 1999 through 2005. The mean age at presentation was 45 years (range, 26-65). Methods: We retrospectively identified patients with NKTL of the ocular adnexa treated in the authors’medical centers from 1999 through 2004 using computerized diagnostic index retrieval. The clinical records and radiologic studies were analyzed to definemodes of presentation and progression, response to therapy, and areas of anatomic involvement. Histopathologic findings, including the presence of CD3, CD56, and Epstein-Barr virus-encoded mRNA in each patient, were reviewed. Main Outcome Measurements: Time of survival from presentation to last known follow-up and tumor-related death. Results: Four of the 8 patients (50%) with NKTL involving the orbit or ocular adnexa had systemic involvement at presentation. Five of the 8 patients (62.5%) had concurrent sinonasal involvement,whereas 3 (37.5%) had orbital involvement alone. All lesions demonstrated CD3, CD56, and/or Epstein-Barr virus positivity on immunopathology studies. Therapy consisted of various chemotherapeutic regimens typically employed in the treatment of non-Hodgkins lymphoma, steroids, surgical intervention, and radiation. Seven (87.5%) patients died 5 weeks to 13 months after presentation, and 1 (12.5%) is alive without disease (5-year follow-up). Conclusions: Natural killer/T-cell orbital lymphoma is a rare Epstein-Barr virus-associated neoplasm that may occur with or without associated sinonasal involvement. Our series, the largest cohort reported to date, demonstrates the high lethality of this condition despite aggressive conventional therapy, suggesting that new treatment options should be considered early in the course of treatment of patients with this disorder. PURPOSE: To review the clinical, radiological, and histopathologic features in 8 patients with natural killer / T-cell lymphoma (NKTL) involving the orbit and / or ocular adnexa, and to describe the responses of these patients to various treatment regimens. Participants: Eight patients (5 male, 3 female) with NKTL involving the orbit and / or ocular adnexa were identified from 1999 through 2005. The mean age at presentation was 45 years (range, 26-65). Methods : We retrospectively identified patients with NKTL of the ocular adnexa treated in the authors’medical centers from 1999 through 2004 using computerized diagnostic index retrieval. The clinical records and radiologic studies were analyzed to define modes of presentation and progression, response to therapy, and areas of anatomic involvement. Histopathologic findings, including the presence of CD3, CD56, and Epstein-Barr virus-encoded mRNA in each patient, were reviewed. Main Outcome Measur ements: Time of survival from presentation to last known follow-up and tumor-related death. Results: Four of the 8 patients (50%) with NKTL involving the orbit or ocular adnexa had systemic involvement at presentation. Five of the 8 patients ( 62.5%) had concurrent sinonasal involvement, 3 (37.5%) had orbital involvement alone. All lesions demonstrated CD3, CD56, and / or Epstein-Barr virus positivity on immunopathology studies. Therapy consisted of various chemotherapeutic regimens typically employed in the treatment of Seven (87.5%) patients died 5 weeks to 13 months after presentation, and 1 (12.5%) is alive without disease (5-year follow-up). Conclusions: Natural killer / T-cell orbital lymphoma is a rare Epstein-Barr virus-associated neoplasm that may occur with or without associated sinonasal involvement. Our series, the largest cohort reported to date, demonstrates the high lethality of this condition despite aggressive conventional therapy, suggesting that new treatment options should be considered early in the course of treatment of patients with this disorder.