Study Objectives: Previous studies have shown sleep-disordered breathing (SDB) to be highly prevalent in patients with idiopathic normal pressure hydrocephalus (iNPH). The current study aimed to estimate and compare the prevalence of SDB in patients with different types of hydrocephalus and test if SDB was associated with changed CO2. Methods: We investigated the prevalence of SDB in a prospective cohort of 48 hydrocephalus patients with nocturnal polysomnography (PSG). Twenty-three of the patients also had simultaneous CO2 measurements. Results: The prevalence of SDB was high in patients with iNPH, with moderate-to-severe SDB in 21/22 (96%) of the patients and an apnea-hypopnea index (AHI) of 43.5 (95% CI 33.8-52.2). Patients with pediatric-onset hydrocephalus had moderate-to-severe SDB in 7/16 (44%), with an AHI of 16.1 (95% CI 8.16-23.8). Except for one patient, all patients with adult-onset obstructive hydrocephalus (9/10) had normal respiration or mild SDB with an AHI of 8.4 (95% CI 5.5-10.5). None of the 23 patients measured with CO2 had elevated CO2 associated with SDB and had normal CO2 during sleep, with 40.8 ± 5.5 mmHg, 42.7 ± 4.1 mmHg, 34.5-45.8 mmHg for patients with iNPH, pediatric-onset, and adult-onset, respectively. Conclusion: We found a high prevalence of SDB in patients with iNPH, confirming previous findings. We extended this with the finding that the prevalence of SDB in patients with other types of hydrocephalus is not significantly different from that in the general population. Additionally, we did not find elevations of CO2 associated with SDB or CO2 retention during sleep. Statement of Significance This study highlights the possible role of sleep-disordered breathing (SDB) in idiopathic normal pressure hydrocephalus (iNPH). Acknowledging, diagnosing, and treating SDB in patients with iNPH could be critical in alleviating the cognitive symptoms, alongside the standard surgical methods used to treat iNPH today. Surgical treatment with a shunt is the only treatment option today, but this treatment is far from optimal. Even after treatment, these patients often have rapid worsening of their symptoms and many complications, leading to additional surgery; thus, additional or alternative treatments are essential. Furthermore, our results suggest that SDB is not caused by hydrocephalus but rather that SDB can play a role in the enigmatic pathogenesis of iNPH and, over time, maybe damage the brain if left untreated.