Purpose <p>Pediatric obstructive sleep-disordered breathing (SDB) is frequently diagnosed using single-night home sleep apnea testing (HSAT). However, concerns persist regarding diagnostic accuracy due to night-to-night variability and the first-night effect, defined as systematic differences between the first and subsequent nights. Previous research on pediatric polysomnography has yielded conflicting findings regarding these phenomena. This study assesses the presence of a first-night effect and quantifies night-to-night variability in respiratory parameters among children undergoing HSAT.</p> Methods <p>This retrospective study analyzed respiratory polygraphy data collected over two consecutive nights from a real-world, unselected population of children with suspected SDB. The primary outcome was the difference in apnea-hypopnea index (AHI) between the first and second nights, commonly referred to as the first-night effect. Secondary outcomes included differences in other respiratory parameters and between-night accuracy in diagnosing obstructive sleep apnea (OSA).</p> Results <p>Forty-eight children (median age: 6.7 years, 75% male) were included in the analysis. No systematic differences were detected between the first and second nights in AHI or other respiratory parameters, suggesting an absence of the first-night effect. Nevertheless, for some participants, measurements varied widely between nights. This resulted in 29% of children changing the diagnostic category of OSA between nights.</p> Conclusion <p>Pediatric HSAT in this real-world population with mostly mild SDB symptoms demonstrates no significant first-night effect; however, moderate night-to-night variability exists in some children. Clinicians must consider this variability when interpreting HSAT results in cases where clinical presentation and single-night HSAT outcomes conflict; a multi-night assessment may be warranted to improve diagnostic accuracy.</p>