Acute tumor lysis syndrome (ATLS) is an entity consisting of combinations of hyperuricemia, lactic acidosis, hyperkalemia, hyperphosphatemia, and hypocalcemia and occurring generally in aggressive, rapidly proliferating lymphoproliferative disorders with high tumor burdens. A patient is described with a diffuse intermediately differentiated lymphocytic lymphoma, considered by most an indolent B-cell non-Hodgkin's lymphoma, in whom developed multiple recurrences of ATLS after treatment when tumor regrowth occurred between cycles of therapy. The mitotic rate of this lymphoma was relatively high (30-80 mitoses/ten high-power fields). Lymph proliferative disorders with a high mitotic rate, and large tumor burden, regardless of histologic features, should be treated prophylactically against tumor lysis if regrowth between cycles occurs.