PURPOSE: To describe sleep-disordered breathing in children with achondroplasia at their first polysomnography (PSG) assessment and examine associations with clinical characteristics. METHODS: This retrospective study included 49 children evaluated between March 2016 and February 2025. Obstructive sleep apnea syndrome (OSAS) was classified using the obstructive apnea-hypopnea index (oAHI). Total AHI was compared according to sex, upper airway surgery history, foramen magnum stenosis, and vosoritide treatment. Infant findings were also presented separately because severity thresholds require cautious interpretation at this age. RESULTS: Median age was 4.48 years (range, 0.22-16.15). OSAS was identified in 39 children (79.6%); 25 (51.0%) met the study criteria for moderate-to-severe disease. Of 15 children without reported sleep-related symptoms, 12 (80.0%) had OSAS, including seven (46.7%) with moderate-to-severe disease. Three children had a central apnea index ≥ 5 events/hour, and two (4.1%) had nocturnal hypoventilation. Total AHI did not differ significantly by sex, surgery history, or foramen magnum stenosis. Median total AHI was 3.2 events/hour in children receiving vosoritide and 6.9 in those not receiving treatment (p = 0.105). CONCLUSION: OSAS was common at the first PSG assessment and was also found in children without reported symptoms. These findings support objective sleep assessment in achondroplasia. The retrospective design and age-dependent interpretation of infant PSG limit conclusions about prevalence and severity; the study cannot establish a respiratory effect of vosoritide. WHAT IS KNOWN: • Achondroplasia increases the risk of obstructive and central sleep apnea. • Reported symptoms may not reliably identify sleep-disordered breathing. WHAT IS NEW: • At first PSG, 12/15 children without reported symptoms had OSAS; 7 had moderate-to-severe disease. • Total AHI did not differ significantly by vosoritide treatment status.