Hypercalcemia is a rare complication of chronic lymphocytic leukemia (CLL), mostly seen in the context of advanced disease, for which different pathogenetic mechanisms have been postulated. A CLL patient who developed hypercalcemia in the setting of Richter's syndrome is reported. She was a 69-year old woman with stage B (II) CLL of 28-month duration, who presented with mental confusion, anorexia, vomiting, and diffuse bone pain, with hypercalcemia being subsequently found. A lymph node biopsy demonstrated evolution of CLL into Richter's syndrome. Serum levels of parathyroid hormone (PTH), PTH-related peptide and several cytokines were normal. The hypercalcemia initially responded to conventional treatment and chemotherapy, but it reappeared coincidentally with disease progression and the development of osteolytic lesions. Richter's syndrome should be kept in mind in CLL patients with hypercalcemia.