A cross-sectional study compared characteristics of homeless adults with and without substance abuse, physical health problems, and history of psycbiatric hospitalization when they first became homeless. Self-report data on demographic characteristics, adverse events in chikihood, and history of medical disorders were collected from 1,399 homeless adults who used three shelters in Santa Clara County, California, during a five-month winter period in 1989 and 1990 (96 percent response rate). A total of 45.6 percent of the respondents reported no impairments when they first became homeless. They were distinguisbed from those with impairments at on set of homelessness by their younger age, minority status, lower educational attainment, and lower frequency of adverse events in childhood. Respondents who reported no impairments when they first became homeless were likely to develop addictive and psychiatric disorders over time. Those who bad been homeless five years or more reported high rates of alcohol abuse (34.5 percent), illegal drug use (24.1 percent), and psychiatric hospitalization (20.7 percent).