In 18 years of experience in the use of combined chemotherapy in Hodgkin's disease at the Instituto Nacional de la Nutrición Salvador Zubirán, the first case of non-Hodgkin's lymphoma secondary to Hodgkin's disease was identified. The patient was a 23 year old male who initially developed a nodular sclerosis type of Hodgkin's disease. Three years later, the biopsies showed lymphocyte predominance type of Hodgkin's disease. Finally, one year later, the patient developed a diffuse small cleaved cell lymphoma. Non-Hodgkin's lymphoma occurring in patients treated with combined chemotherapy and radiotherapy after Hodgkin's disease is a rare complication. We believe that the genesis of a second neoplasm in these cases may be due to both disturbances in the cellular immunity intrinsic to Hodgkin's disease and the treatment with combined chemotherapy and radiotherapy.