Introduction: The diagnosis of obstructive sleep apnea (OSA) is routinely based on just a single night's sleep examination. The night-to-night variability in children and adolescents has previously been investigated using type 4 sleep monitors or PSG. However, there is a lack of studies investigating the night-to-night variability when using type 3 sleep monitors. Therefore, the main purpose was to investigate the night-to-night variability in respiratory parameters in children and adolescents using a portable type 3 monitor. Furthermore, the purpose was to investigate the clinical relevance of night-to-night variability. Methods: The study population was recruited from an ongoing research project concerning the effect of weight loss in children and adolescents with OSA and overweight/obesity. The inclusion criterion was the successful recording of two consecutive nights of sleep. Sleep examinations were recorded at home using the Nox T3 device and then blindly scored by the same registered polysomnographic technologist. To compare the respiratory parameters measured each night, a paired t-test or a Wilcoxon signed-rank test was used. The apnea-hypopnea index (AHI) was further described graphically with a scatter plot and a Bland-Altman plot. The presence and severity of OSA were described in tables. Results: A total of 30 children and adolescents with a median age of 14.8 years were included. When comparing respiratory parameters between nights, all p-values derived from paired t-tests and Wilcoxon signed-rank tests were >0.05. When considering the graphical depictions of AHI, it was evident that for some participants AHI measurements varied widely from night to night. Regarding the presence of OSA, 27% of participants changed diagnostic category between nights and 40% of those with a normal AHI on the first night had OSA on the second night. Regarding OSA severity, 50% of participants changed severity category between nights. Conclusions: AHI measurements varied widely between nights in some children and adolescents leading to frequent changes in both diagnosis and severity of OSA from night to night. We therefore suggest the presence of a clinically relevant night-to-night variability which should be taken into account when diagnosing pediatric OSA.