['To determine the emergency department (ED) environmental factors associated with patient satisfaction.', 'A prospective, observational study in a university-affiliated tertiary-referral ED and associated observation unit (OU). The ED environment was evaluated with a structured questionnaire, scored using a 100-mm visual analogue scale. Patients who stayed in the ED over 8 h (long-stay ED; LSED) were compared with those who stayed less than 4 h (short-stay ED; SSED) and with a control group admitted to the OU.', 'A total of 233 patients was enrolled, overall satisfaction in SSED was 81% (95% CI 70.1 to 88.7), 69% in LSED (95% CI 57.4 to 78.7) and 84% in OU (95% CI 73.6 to 91.0). The most important environmental factors were cleanliness (median importance 95, interquartile range (IQR) 81-98) and communication with medical staff (94, IQR 80-98) and family (92, IQR 74-98). The least important factors were access to nature (38, IQR 19-65), a natural light source (50, IQR 24-74) and ability to sit out of bed (52, IQR 26-75). Factors rated high for importance but low for satisfaction were ED noise levels (median difference 40, IQR 3-70), ED trolley comfort (19, IQR 6-50) and food quality (12, IQR -4-29).'] Does satisfaction with the emergency department environment decrease with length of stay?