Burkitt lymphoma (BL) is a rare neoplasm constituting 1-2% of adult lymphomas. Our aims in this study were to establish prognostic factors for overall survival in adult BL and evaluate the efficacy of different chemotherapy regimens in a population based setting. The study population was collected from the Swedish Lymphoma Registry 2000-2010. During this period, 156 adult patients with BL were identified. In multivariate analysis, age and performance status (PS) were significant adverse prognostic factors for overall survival. A modified prognostic index, based on: age >40 years, PS >1, and lactate dehydrogenase > upper limit of normal (ULN) was proposed. Patients with a score of 0-1, 2, and 3 were found to have a 2-year survival of 91.2%, 58.4%, and 27.5%, respectively. High-intensity regimens were associated with more favorable overall survival. Rituximab addition was not significantly associated with improvement in survival. A modified prognostic index may be valuable for adult BL, as proposed.