Older adults represent the highest proportion of gamblers (Ontario Lottery and Gaming Corporation [OLG], 2012). Unpartnered older adults may be more socially isolated and lonely (Dykstra & de Jong Gierveld, 2004), thus more likely to be at risk for problem gambling (McQuade & Gill, 2012). We examined whether gambling to socialize or from loneliness and going to the casino with friends/family mediate the relation between marital status and problem gambling. Data from a random sample of older adults at gambling venues across Southwestern Ontario indicated that gambling with family/friends and gambling due to loneliness mediated the relationship between marital status and problem gambling. Relative to those married, unpartnered older adults were less likely to gamble with family/friends, more likely to gamble due to loneliness, and had higher problem gambling. Prevention and treatment initiatives should examine ways to decrease loneliness and social isolation among older adults and offer alternative social activities.