Mental illness affects a broad range of Canadians. Most people with compromised mental health are not homeless, and many people who are homeless have never been diagnosed with a mental illness. However, new analyses of CIHI data show that in 2005-2006, 35% of visits by homeless people to surveyed hospital emergency departments (mostly in Ontario) were due to mental and behavioral disorders. The most common type of disorder was psychoactive substance abuse, which accounted for 54% of visits (62% for homeless men and 30% for homeless women), followed by other psychotic disorders and delusional disorders (accounting for 20% of visits). Among non-homeless patients, injury, poisoning and consequences of external causes was the most common reason, accounting for 25% of ED visits.