Specialized transitional shelters are available in various cities to provide assistance to homeless individuals with serious mental illness. Little is known about the population using such shelters. The authors conducted a retrospective chart review to collect demographic, social, and clinical data of residents in a state-operated mental health transitional shelter in Massachusetts. A total of 74 subjects were included. Schizophrenia-spectrum disorders were present in 67.6 % of the sample and mood disorders in 35.1 %. Substance use disorders were documented in 44.6 %. Chronic medical illness (mostly hypertension, dyslipidemia, asthma, and diabetes) was found in 82.4 %. The co-occurrence of a psychiatric and substance use disorder and chronic medical illness was found in 36.5 %. The majority (75.7 %) of patients had a history of legal charges. Homeless individuals with serious mental illness served by specialized transitional shelters represent a population with complex psychiatric, medical and social needs.