Objectives: To determine effects of quetiapine on polysomnographicrecorded sleep architecture and parameters. Introduction and Hypothesis: Quetiapine receptor profile suggests that sleep-inducing and sleep-modifying properties may be causing changes in sleep architecture and parameter, which may have therapeutic value. Methods: A cross-sectional retrospective study conducted at the sleep center. Polysomnographic sleep records were selected and reviewed from among patients who presented over 24-months for evaluation. Twenty-one patients were selected and matched based on age, sex, body-mass index (BMI), and the presence/absence of obstructive sleep apnea (OSA) to control subjects without quetiapine. Correlation analysis was performed to assess the association of quetiapine with sleep architecture and parameters. Results: Quetiapine was not significantly associated with altered sleep efficiency, sleep latency, wake time after sleep onset, or the relative percentage of sleep stages. A notablebut not significant (p = 0.08), increase in the rapid eye movement latency was observed. Conclusions: Among the study population quetiapine was not found associated with changes in sleep architecture and parameters. Hypothesis : Use of quetiapine will be associated with shortened sleep latency (SL), increased total sleep time (TST), and increased non-rapid eye movement (NREM) stage III (most restorative sleep).