Little is known about risk factors for problem gambling (PG) within the rapidly growing urban Aboriginal population in North America. Racial discrimination may be an important risk factor for PG given documented associations between racism and other forms of addictive behaviour. This study examined associations between racial discrimination and problem gambling among urban Aboriginal adults, and the extent to which this link was mediated by post traumatic stress. Data were collected via in-person surveys with a community-based sample of Aboriginal adults living in a mid-sized city in western Canada (N = 381) in 2010. Results indicate more than 80 % of respondents experienced discrimination due to Aboriginal race in the past year, with the majority reporting high levels of racism in that time period. Past year racial discrimination was a risk factor for 12-month problem gambling, gambling to escape, and post traumatic stress disorder (PTSD) symptoms in bootstrapped regression models adjusted for confounders and other forms of social trauma. Elevated PTSD symptoms among those experiencing high levels of racism partially explained the association between racism and the use of gambling to escape in statistical models. These findings are the first to suggest racial discrimination may be an important social determinant of problem gambling for Aboriginal peoples. Gambling may be a coping response that some Aboriginal adults use to escape the negative emotions associated with racist experiences. Results support the development of policies to reduce racism directed at Aboriginal peoples in urban areas, and enhanced services to help Aboriginal peoples cope with racist events.