Of 27,638 homeless adults admitted to Philadelphia public shelters in the years 1990 through 1992, 20.1% received treatment for a mental health disorder, and 25.3% for a substance use disorder in the years 1985 through 1993. An additional 20.7% were identified as having untreated substance use problems. Overall, a total of 65.5% of adult shelter users were identified as ever having had a mental health or substance use problem, treated or untreated.