A rich body of literature attests to the importance of affordable accommodation and support services necessary, appropriate, and acceptable to persons disabled by amental illness.However, there is a little which provides a means for housing and service planners to determine the gap between available supportive housing and need. Such understandings are needed to prepare strategies and develop the resources needed to accommodate persons with a disabling mental illness in the community. While housing studies that examine shelter needs of the homeless acknowledge that a sizable proportion has a disabling mental illness, these numbers underestimate need in the cohort that experiences disablingmental illnesses.This underestimate exists because many of those who are disabled by mental illness and in need of supportive housing are among the hidden homeless: doubled-up, couch-surfing, and temporarily sheltered by friends and family.Thus, little is known about the size of this cohort or their supportive shelter needs. The present analysis examines two approaches and offers one methodology as most feasible and parsimonious which can approximate housing need and may be extrapolated to other urban locations.