The goal of this study was to evaluate the influence of obstructive sleep apnoea on the severity and short-term prognosis of patients admitted for acute coronary syndrome. Obstructive sleep apnoea was defined as an apnoea–hypopnoea index (AHI) >15 h−1. We evaluated the acute coronary syndrome severity (ejection fraction, Killip class, number of diseased vessels, and plasma peak troponin) and short-term prognosis (length of hospitalisation, complications and mortality). We included 213 patients with obstructive sleep apnoea (mean±SD AHI 30±14 h−1, 61±10 years, 80% males) and 218 controls (AHI 6±4 h−1, 57±12 years, 82% males). Patients with obstructive sleep apnoea exhibited a higher prevalence of systemic hypertension (55% versus 37%, p<0.001), higher body mass index (29±4 kg·m−2 versus 26±4 kg·m−2, p<0.001), and lower percentage of smokers (61% versus 71%, p=0.04). After adjusting for smoking, age, body mass index and hypertension, the plasma peak troponin levels were significantly elevated in the obstructive sleep apnoea group (831±908 ng·L−1 versus 987±884 ng·L−1, p=0.03) and higher AHI severity was associated with an increased number of diseased vessels ( p=0.04). The mean length of stay in the coronary care unit was higher in the obstructive sleep apnoea group ( p=0.03). This study indicates that obstructive sleep apnoea is related to an increase in the peak plasma troponin levels, number of diseased vessels, and length of stay in the coronary care unit.