Housing quality (HQ) is associated with mental health, and may mediate outcomes in housing interventions. However, studies of housing interventions rarely report HQ. The purpose of this study was to describe HQ in a multi-site randomized controlled trial of Housing First (HF) in five Canadian cities and to examine possible differences by treatment group (HF recipients and treatment-as-usual (TAU) participants who were able to find housing through other programs or on their own). We also examined the association between HQ and the primary trial outcome: housing stability. The performance of a new multi-dimensional standardized observer-rated housing quality scale (the OHQS) in a relatively large cross-site sample was also of interest. HQ was rated by trained research assistants for 204 HF participants and 228 TAU participants using the OHQS. General linear regression models were used to examine unit/building quality scores by group and site adjusting for other group differences, and as a predictor of housing stability outcomes after 24 months of follow-up. The OHQS was found to have good reliability and validity, but because most of the neighborhood subscale items were negatively correlated with the overall scale, only unit and building items were included in the total HQ score (possible scores ranging from 13.5 to 135). Unit/building HQ was significantly better for the HF group overall (91.2 (95 % CI = 89.6-92.9) vs. 88.3 (95 % CI = 86.1-90.5); p = .036), and in one site. HQ in the TAU group was much more variable than the HF group overall (W (mean) = 24.7; p G .001) and in four of five sites. Unit/building HQ scores were positively associated with housing stability:
682CI 91.4-94.9)) for those housed all of the time (F = 43.9 p G .001). This association held after adjusting for site, housing characteristics, participant ethnocultural status, community functioning, and social support. This study demonstrates that HQ can be as good or better, and less variable, in HF programs in Canada that systematically and predominantly source housing stock from the private sector compared to housing procured outside of an HF program. HQ is also an important predictor of housing stability outcomes.