Background: Across the circumpolar north, Inuit experience high level of inadequate, overcrowded housing. This study examines whether household crowding and the social structure of the household are associated with mental symptoms and comorbid behaviours among Inuit in Greenland. Methods: Data on 3108 Inuit aged 18 years and older are from the Inuit Health in Transition Survey. Dependent variables considered were: feelings of depression and of anxiety; binge drinking; harmful drinking; and use of marijuana. Household crowding was measured by the number of people in the house, and the social structure by the adult to children composition of the household. Logistic regression models were adjusted for respondents’ age, sex, marital status and socioeconomic circumstances. Analyses were stratified by sex. Results: In the total sample, increased number of person in the house was associated with higher risk of reporting feeling anxious (OR: 1.05; 95%CI: 1.00-1.09) or depressed (OR: 1.05; 95%CI: 1.02-1.09), but with lower risks of heavy drinking (OR: 0.89; 95%CI: 0.82-0.98), use of marijuana (OR: 0.85; 95%CI: 0.77-0.94), and marginally (p<0.10) with harmful drinking (OR: 0.92; 95%CI: 0.84-1.01). These associations were explained when considering the social structure of the household. Compared to households with children, the risk of feeling depressed was less likely among people living in ‘adult-only’ households (OR: 0.81; 95%CI: 0.66-0.97). The risk of binge drinking (OR: 1.99; 95%CI: 1.65-2.42) and using marijuana (OR: 1.34; 95%CI: 0.98-1.81), but not of harmful drinking, were significantly higher in households composed only of adults. Although similar patterns of associations are observed, household crowding and the social structure of the household appear to influence women’s mental symptoms and comorbid behaviours to a greater extent than they do for men. Conclusion: Exposure to chronic stress of living in inadequate overcrowded households contributes to explaining the high prevalence of mental symptoms and comorbid behaviours among Inuit. The presence of children in the house appears to act as a ‘regulator’ of unhealthy behaviours. Reducing household crowding, through housing policies, is likely a key strategy to improve Inuit mental health. Health promotion actions might also be more effective if targeting groups of people distinguished by their living conditions, e.g. targeting cohabiting adults without children or single women with dependent children.