Purpose <p>The relationship between obesity hypoventilation syndrome (OHS) and traffic accidents has not been previously studied. We aimed to determine the frequency of traffic accidents and the associated risk factors among people with OHS and compare with obstructive sleep apnoea (OSA) individuals.</p> Methods <p>We screened patients diagnosed with OSA and/or OHS in our sleep laboratory between 2015 and 2023. Patients who had a driver’s license, had been driving for at least five years, at least three days a week, and drove more than 5000&#xa0;km/year and had not received positive airway pressure treatment prior to their diagnosis were included. Polysomnographic data, the Epworth Sleepiness Scale (ESS), the Berlin Sleep Questionnaire were collected from the records. The Fatigue Assessment Scale (FAS) and inattention scores before the diagnosis, driving information and accident numbers from the three years before the diagnosis to the phone call were evaluated.</p> Results <p>A total of 121 patients (OHS/OSA: 43/78, F/M: 5/116, age: 46.9 ± 9.7 years, body mass index [BMI]: 32.5 ± 5.7&#xa0;kg/m²) were included. ESS, FAS, apnoea-hypopnea index (AHI), oxygen desaturation index (ODI) and percentage of total sleep time with SpO₂ less than 90% were significantly greater in OHS patients (<i>p</i> = 0.012, <i>p</i> = 0.028, <i>p</i> = 0.003, <i>p</i> = 0.002 and <i>p</i> = 0.021, respectively). The frequency of accidents was greater in OHS patients than in OSA patients (46.5% vs. 26.9%, <i>p</i> = 0.029). In the multivariate analysis, only BMI was an independent factor (OR: 1.185, 95% CI: 1.005–1.396, <i>p</i> = 0.044).</p> Conclusion <p>Traffic accidents were more common in OHS patients than in OSA patients, with obesity as the primary independent risk factor.</p>