We report a male Japanese with corticotropin (ACTH)-independent macronodular adrenocortical hyperplasia (AIMAH) associated with multiple colon adenomas/carcinomas. The plasma cortisol level was elevated with no diurnal rhythm and was not suppressed with dexamethasone. Basal plasma ACTH was unmeasurable but subnormally increased after administration of metyrapone or corticotropin releasing hormone. Both adrenals were resected and weighed 90g; the histopathologic findings were similar to those of AIMAH as previously reported. At least 21 colon lesions which were adenomas or carcinomas, were resected endoscopically or surgically. This is the second reported case of the association of AIMAH with multiple colon polyps. An APC gene point mutation was detected in the colon cancer tissue by polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP)/direct sequencing analysis at the putative splice acceptor site consensus sequence. However, no abnormality of APC gene was detected in the adrenocortical hyperplastic tissue. The possible etiological coexistence of these two diseases is discussed.