Cancer is primarily a chronic disease of older adults that must be managed and incorporated into everyday activities. Online sites are important sources of health care information and support. Health literacy is necessary for full utilisation of online resources. The objective of this study was to examine and compare cancer related conversations in online forums hosted by Canadian and American associations for retired persons. A content analysis was used to evaluate archived cancer conversations of general-health online forums representing two leading North American associations for retired persons. There were 125/1817 (6.8%) Canadians and 70/892 (7.8%) US cancer discussions among participants in 2006. Online conversations were grouped into three categories: request for information, provision of information and sharing of information. Important subthemes included cancer prevention and screening, treatment and cancer care and health system issues. There were significantly more posts about provision of cancer information from the Canadian compared with the US site (p = 0.023). American more than Canadian conversations emphasised the health system concerns as determinants of cancer care practices. Online discussion forums hosted by retirement associations may serve as an important channel in information dissemination about cancer prevention and screening, treatment and care support and health care advice for seniors.