The risk of a second cancer was assessed in 1,152 patients with Hodgkins disease who were treated at the Norwegian Radium Hospital from 1968-85. 68 patients developed a second cancer more than one year after the diagnosis of Hodgkins disease. These included nine acute non-lymphocytic leukemias, eight non-Hodgkins lymphomas and 51 solid tumours, including 11 lung cancers. The overall relative risk (observed/expected ratios) of developing a second cancer was 1.86. After 18 years the cumulative risk of developing a second cancer was 14.4% +/- 2.9%, of which 11.2% +/- 2.6% referred to solid tumours. The cumulative risk of leukemia appeared to reach a plateau level of 1.5% after 12 years while the risk of non-Hodgkins lymphomas and lung cancer continued to rise with time to 2.1% and 3.3% respectively after 18 years. The risk of developing leukemia increased after treatment with alkylating agents and Procarbazine. The risk of non-Hodgkins lymphoma was not related to any specific type of therapy. Excess lung cancer risk was noted in patients treated with radiotherapy, and the cancers appeared within the treated areas.