OBJECTIVE To determine the incidence of a second malignancy in patients with Hodgkin's disease (HD) diagnosed and treated in the same hospital. METHODS A retrospective study was performed on 99 patients diagnosed and treated for HD in the Hospital San Carlos, in Madrid, between January 1976 and december 1987. The clinical records were revised; the diagnosis and staging followed the Rye and Ann Arbor criteria, and the treatment included radiation therapy (RT), chemotherapy (CT), or a combination of both. The diagnosis of the second malignancy was based upon clinical, analytical, radiological and histological records. RESULTS The median age in the series was 31 years (16-82) and the M/F ratio was 61/38. The stage distribution was: I-9; II-29; III-31, and IV-30. Twenty-six patients received RT alone, 59 were treated with CT, and 14 received RT plus CT. A second neoplasm was found in 6 patients (6%), of whom 4 developed a myelodysplastic syndrome (MDS) and 2 a solid tumour. All the patients who had MDS had received MOPP or C-MOPP chemotherapy, associated in two of them with extensive RT. Both patients with solid tumour had been given CT+RT. The median time of presentation of the second malignancy since the diagnosis od HD was 89 months (48-174) for MDS and 120 months for the solid tumours. The four MDS patients have died, 2 for ANLL-M5, one for SRA and the remainder for cerebral haemorrhage, not yet evolved into acute leukaemia. The two patients which solid tumours are alive and seemingly in complete remission at 12 and 10 months, respectively, of the diagnosis of the second malignancy. CONCLUSIONS 1) All the patients with second neoplasms had been previously treated with CT (MOPP or C-MOPP) or CT+RT. 2) Non-Hodgkin's lymphoma has not appeared in any of the patients in this series. 3) An endless follow-up of patients with HD seems important in order to achieve an early diagnosis of other malignant complications which, although in case of MDS have poor prognosis, in case of solid tumours may do well with adequate treatment.