Syndrome of inappropriate antidiuretic hormone secretion is frequent in small-cell lung carcinomas. We report on a case of syndrome of inappropriate antidiuretic hormone secretion after each of the first 2 cycles of chemotherapy for small-cell lung cancer. The association with chemotherapy-induced tumor lysis is proposed, particularly based on the course of antidiuretic hormone levels, and a review of the literature is presented. Syndrome of inappropriate antidiuretic hormone secretion can occur during tumor lysis syndrome.