A 27-year old man with cystic fibrosis was found to have adenocarcinoma of the colon. He developed an intestinal obstruction due to colocolic intussusception with the tumor in front. The tumor could be totally resected surgically. The patient died 6 months later due to cardiorespiratory failure. Malignant diseases are rare in cystic fibrosis. The most frequent reported malignancies are tumors of the gastrointestinal tract and leukemias or lymphomas. There appeares to be an increased risk for adults with cystic fibrosis to develop gastrointestinal tumors.