This study examines the demographic and physical and mental health characteristics of social work clients among cancer patients in Canada as compared with nonusers of social work services, and factors that affect use of social work services among cancer patients. On the basis of data from two cycles of the Canadian Community Health Survey, the study's samples include 2,703 and 2,821 Canadians living with cancer in 2000-01 and 2003, respectively. The number of Canadians with cancer who consulted social workers about their physical, emotional, or mental health increased from 31,005 to 36,427 over the study period. Results indicate that cancer patients who used social work services were in need of social support or were members of vulnerable populations. Patient's age, living arrangement, income, depression status, and physical limitations were significant predictors of service use. Findings of this study, never reported before, offer information important for identifying barriers to service use and for future planning of social work services and resources.