<p>High-risk issues, such as overdose, suicidality, hoarding, violence, property damage, and apartment takeovers, are known challenges in supportive housing and Housing First programs. However, the effects of these incidents on residents, service providers, and programs have been minimally studied. The objective of this mixed-methods study was to understand what service providers perceived as the impacts of various high-risk issues in supportive housing and Housing First programs, with an emphasis on housing tenure. This descriptive study used an exploratory sequential mixed-methods design, with unequal weighting (QUAL→quan). In-depth interviews were held with 32 service providers working in supportive housing and Housing First programs, followed by an online survey of 202 additional service providers across Canada. In the qualitative dataset, high-risk issues were identified as having three types of potentially harmful impacts: [1] “we have to evict certain people sometimes” (residents’ housing stability); [2] “we’re exposed to these traumas as well” (service providers’ mental health); and [3] “we’re losing our stock, basically” (organizational relationships with landlords and access to housing units). Convergence was generally found in the quantitative findings, with high-risk issues affecting other individuals and property being perceived as more likely to cause housing loss. Service providers working in scattered-site programs reported that hoarding, overdose, and apartment takeovers were significantly more likely to cause housing loss than did participants of single-site programs. Overall, study findings underscore how high-risk issues, particularly those affecting others and property, can be potential housing trajectory-altering events and that this is further shaped by housing and support models.</p>