A family history of colorectal cancer may increase colorectal cancer risk by influencing adenoma growth or enhancing the formation of new lesions. Data of men from the prospective Health Professionals Follow-Up Study who underwent an endoscopy between 1986 and 2004 were used to evaluate whether a family history of colorectal cancer is associated with adenoma multiplicity or advanced adenoma stage (> or =1 cm, histology with villous component or carcinoma in situ). 21.4% of the 3,881 adenoma patients and 13.9% of the 24,959 adenoma-free men had a first-degree relative with colorectal cancer. Thousand four hundred and ninety-six men were classified as having advanced and 1,507 as having nonadvanced adenomas. Six hundred and twenty-two men had multiple and 1,985 had single adenomas in the distal colon and rectum. A family history of colorectal cancer was similarly associated with advanced and nonadvanced adenomas [multivariable odds ratio (OR) (95% confidence interval): advanced vs. nonadvanced, 0.98 (0.82-1.17), advanced vs. adenoma-free: 1.67 (1.47-1.91), nonadvanced vs. adenoma-free: 1.70 (1.49-1.94)], although potential differences according to adenoma location were seen. A family history of colorectal cancer was more strongly associated with multiple distally located adenomas [odds ratio (95% confidence interval): multiple vs. single, 1.35 (1.09-1.68), multiple vs. no distally located adenomas: 2.02 (1.67-2.44), single vs. no distally located adenomas: 1.49 (1.32-1.68)]. The number of adenomas was also positively associated with a family history of colorectal cancer. Our findings suggest that at the population level, heritable factors may be more important in earlier stages of adenoma formation than at stages of adenoma advancement for at least distally located adenomas.