OBJECTIVE: Sleep quality is essential for health, with sleep deprivation linked to physical and mental issues. Homeless populations face additional sleep challenges, yet this topic remains underexplored. This study assessed sleep quality among homeless individuals in São Paulo, Brazil, considering demographics and substance use. METHODS: A psychiatrist conducted interviews to collect demographic and substance use data assessing sleep quality using the Pittsburgh Sleep Quality Index (PSQI). A Generalized Linear Model analyzed PSQI scores, considering sleeping location, gender, substance use, and interactions as fixed factors, with homelessness duration as a covariate. The sample comprised 177 participants (22% female, 7 transgenders
mean age: 42.8 ± 11.4 years), with an average homelessness duration of 10.5 ± 8.4 years (range: 1-40). Among them, 33% slept in shelters, 83% used depressants, 83% stimulants, and 59% hallucinogens. RESULTS: Approximately 67% reported good subjective sleep quality (mean PSQI: 4.9 ± 2.7). Depressant and stimulant use correlated with poorer sleep. Women had poorer sleep, longer sleep latency, and greater daytime dysfunction than men. CONCLUSIONS: Positive sleep quality reports may reflect adaptive expectations from prolonged adversity and substance use. The findings highlight the need for improved shelters and targeted interventions to address sleep challenges in this vulnerable population.