Summary Recent studies indicate that ambient temperature may modulate obstructive sleep apnoea (OSA) severity. However, study results are contradictory warranting more investigation in this field. We analysed 19,293 patients of the European Sleep Apnoea Database (ESADA) cohort with restriction to the three predominant climate zones according to the Köppen–Geiger climate classification: Cfb (warm temperature, fully humid, warm summer), Csa (warm temperature, summer dry, hot summer), and Dfb (snow, fully humid, warm summer). Average outside temperature values were obtained and several hierarchical regression analyses were performed to investigate the impact of temperature on the apnea–hypopnea index (AHI), oxygen desaturation index (ODI), time of oxygen saturation <90% (T90) and minimum oxygen saturation (MinSpO 2 ) after controlling for confounders including age, body mass index, gender, and air conditioning (A/C) use. AHI and ODI increased with higher temperatures with a standardised coefficient beta ( β ) of 0.28 for AHI and 0.25 for ODI, while MinSpO 2 decreased with a β of −0.13 (all results p < .001). When adjusting for climate zones, the temperature effect was only significant in Cfb (AHI: β = 0.11) and Dfb (AHI: β = 0.08) (Model 1: p < .001). The presence of A/C (3.9% and 69.3% in Cfab and Csa, respectively) demonstrated only a minor increase in the prediction of the variation (Cfb: AHI, R 2 +0.003; and Csa: AHI, R 2 +0.007; both p < .001). Our present study indicates a limited but consistent influence of environmental temperature on OSA severity and this effect is modulated by climate zones.