Sleep-related disorders are responsible for many serious health conditions, one of these being sleep apnea syndrome, which arises through various mechanisms. Polysomnography is currently used as the gold standard method for diagnosing patients suffering from sleep breathing disorders, thus enabling accurate and swift clinical diagnosis. Background/Objectives: By using the parameters obtained from polysomnography, this retrospective study has aimed to determine the groups of children that are particularly vulnerable to severe forms of breathing disorders, divided according to diagnoses made of tonsillar hypertrophy forms and sleep apnea as well as by the severity grades and types of apnea, to facilitate rapid and appropriate treatment. Methods: The subjects were 419 children (from 2017 to 2024) who had been initially diagnosed with sleep apnea syndrome (36.99% girls and 63.01% boys), upon whom various parameters of polysomnography examinations were retrospectively evaluated. The subjects were broken down into groups according to three diagnoses and the types and severities of apnea. The following statistical analyses were used: Kruskal–Wallis tests, post-hoc testing and correlation. Results: Tonsillar hyperplasia was found in 334/419 subjects. The total apnea incidence was highest in the total mild severity grouping (53.33%), while the highest total apnea incidence in the apnea type grouping was found in the central apnea grouping at 31.74%, of which the highest sub-group incidence of apnea was found in those with the mild form (25.54%). The highest incidence of apnea was found in its mild form in subjects with pharyngeal and palatine tonsil hypertrophy (19.57%). The highest apnea incidence for those initially diagnosed with sleep apnea was 10.74% for the central apnea type. Children with hypertrophy of the pharyngeal tonsil and palatine tonsils had the more severe form of apnea than in the other cases in terms of AHI. Apnea severity, AHI, ODI and BS below 89% were highest/longest in the peripheral apnea type, whereas the REM sleep time %-age was lowest in this type. Strong positive correlations were found between AHI with ODI and sleep time below 89%, whereas strong negative correlations were found between AHI with average and minimum saturation variables. Conclusions: Polysomnography findings of especially mild or severe sleep apnea in children with tonsillar hyperplasia should indicate that surgical treatment is needed as soon as possible. Keywords: sleep apnea syndrome; polysomnography; sleep study; children