The first night effect during polysomnography, and patients’ estimates of sleep quality

•The in-laboratory polysomnography study showed significant “first night effect” (sleeping worse) and “reverse first night effect” (sleeping better), but with varying rates in different sleep disorders.•48.9% of patients had first night effect, 30.5% slept as usual, and 20.6% had reverse first night effect.•These results are useful as a reference for interpretation of nocturnal in-laboratory PSG results in different sleep disorder. We surveyed patients the next morning after in-laboratory polysomnography (PSG) to compare the first night effect (FNE) and reverse first night effect (RFNE) in different sleep disorders. A questionnaire was given to 852 patients with insomnia (n = 171), restless legs syndrome (n = 186), obstructive sleep apnea (n = 369), simple snoring (n = 54), REM sleep behavior disorder (n = 39), and hypersomnia (n = 33). FNE was seen in 48.9%, 30.5% slept as usual, and 20.6% had RFNE. The highest incidences of FNE were seen in OSA, simple snoring, hypersomnia, and in men. We propose to use these findings as a reference when interpreting nocturnal in-laboratory PSG results.