To investigate the factors influencing the malignant potential of adenomas, a logit analysis was carried out. The malignancy rate (frequency of malignant areas infiltrating into submucosa) in adenomas is influenced by 1. the size of the adenoma, 2. the interrelationship between size and histological type (tubular, tubulo-villous, villous) and 3. the macroscopic growth pattern (pedunculated, semipedunculated, sessile). No influence is exercised by the number of adenomas, their localization, or the sex of the patient.