Background: The impact of removing the upper airway lymphoid tissue and in particular, tonsillectomy, in adults with OSA has not been demonstrated in large populations. Aims: To compare the severity of OSA and the prevalence of cardiovascular, metabolic and respiratory co-morbidities between patients with OSA who had undergone previous tonsillectomy and those who had not. Methods: The 19,711 participants in this study came from the European sleep apnea database (ESADA) which comprises data from unselected adult patients aged 18-80 years with a history of symptoms suggestive of OSA referred to sleep centers throughout Europe. Results: There were no differences between the two groups in terms of sex ratio and age (146 patients with previous tonsillectomy vs. 19565 patients without). Patients who had undergone tonsillectomy had a lower body mass index (29.3 ± 5.2 kg/m2 vs 32.2 ± 6.6 kg/m2, p < 0.001), lower subjective sleep latency (17.1 ± 17.8 min vs 25.5 ± 30.4 min, p = 0.001), lower ODI (15.7 ± 18.3 events/hour vs 30.7 ± 26.1 events/hour, p < 0.001), and SpO2<90% time during sleep (21.8 ± 47.5 min vs 52.6 ± 80.8 min, p < 0.001). OSA patients with tonsillectomy had a lower prevalence of Type II diabetes mellitus (p = 0.001), hypertension (p < 0.001) and a higher prevalence of hyperlipidemia (p < 0.001) and were less likely to be commenced on CPAP (p < 0.001). Conclusion: In a large population of almost 20,000 OSA patients from across Europe, patients who had undergone tonsillectomy presented with less severe OSA at time of diagnosis, and had a lower prevalence of Type II diabetes mellitus and cardiovascular co-morbidities.