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Sound levels in the intensive care unit (ICU) are universally elevated and are believed to contribute to sleep and circadian disruption. The purpose of this study is to compare overnight ICU sound levels and peak occurrence on A- vs C-weighted scales.This was a prospective observational study of overnight sound levels in 59 medical ICU patient rooms. Sound level was recorded every 10 seconds on A- and C-weighted decibel scales. Equivalent sound level (Leq) and sound peaks were reported for full and partial night periods.The overnight A-weighted Leq of 53.6 dBA was well above World Health Organization recommendations; overnight C-weighted Leq was 63.1 dBC (no World Health Organization recommendations). Peak sound occurrence ranged from 1.8 to 23.3 times per hour. Illness severity, mechanical ventilation, and delirium were not associated with Leq or peak occurrence. Equivalent sound level and peak measures for A- and C-weighted decibel scales were significantly different from each other.Sound levels in the medical ICU are high throughout the night. Patient factors were not associated with Leq or peak occurrence. Significant discordance between A- and C-weighted values suggests that low-frequency sound is a meaningful factor in the medical ICU environment.