The clinical, pathological and biologic features of 79 mucinous colorectal carcinomas were compared with those of 602 non-mucinous adenocarcinomas. The two groups did not show appreciable differences in patients' age, stage distribution, extent of lymph node involvement, grade of differentiation, pattern of growth and venous invasion. Mucinous carcinomas occurred more frequently among female patients (P < 0.05) and in the proximal colon (P < 0.01). Moreover, mucinous carcinomas more often demonstrated origin within villous adenomas (P < 0.0001) and lacked pronounced peritumoural lymphocytic infiltration (P < 0.001). A strong association was found between tumour type and flow cytometric nuclear DNA content. A high proportion of mucinous carcinomas showed DNA index (DI) values < or = 1.20 (26/38, 68.4%); conversely only 103 of 322 (32%) non-mucinous carcinomas had a DI < or = 1.20 (P < 0.0001). In addition mucinous carcinomas were characterized by infrequent p53 overexpression (4/21, 19% versus 120/183, 65.6%; P < 0.001) and higher levels of proliferative activity (P < 0.0001) compared to non-mucinous adenocarcinomas. Our data support the hypothesis that mucinous carcinoma represents a distinct clinicopathologic and genetic entity.