: Chronic rhinosinusitis with nasal polyps (CRSwNP) is a chronic upper airway disease that may involve different inflammatory endotypes, although in Western populations it is most commonly associated with type 2 inflammation. CRSwNP has a significant impact on the patient's quality of life. The recommended appropriate medical therapy is effective in controlling CRSwNP symptoms in many patients; however, a subset continues to exhibit persistent type 2 inflammation, evidenced by recurrent nasal polyps, elevated eosinophil counts, or the need for systemic corticosteroids or surgery. Monoclonal antibodies have recently become a novel and personalized treatment that can help refractory patients restore disease control. : The present study aims to evaluate the effectiveness of mepolizumab in real-world settings in a diverse patient population, focusing on assessing the impact of this therapy on patient-reported outcomes after six months of treatment. This is a multicenter, observational study of CRSwNP patients treated with mepolizumab carried out in five hospitals located in Spain. Adult patients with a diagnosis of uncontrolled CRSwNP were included in the study. The change in the nasal polyp score (NPS) was the main clinical endpoint. Changes in the Sinonasal Outcome Test (SNOT-22), nasal congestion and smell impairment visual analogue scale scores, and blood and nasal polyp tissue eosinophil counts were among other endpoints included. : In total, 47 patients were included, and 91% were asthmatic. The nasal polyp score (0-8) was reduced significantly in the cohort (mean change: -2.56, < 0.0001). The mean SNOT-22 score improved 25.29 points. Nasal congestion (-3.57, < 0.0001) and smell impairment (-4.0, < 0.0001) visual analog scale scores (0-10) showed a significant improvement. Blood and tissue eosinophil median counts showed significant reductions versus baseline of 86% and 26%, respectively. Among those patients with asthma, the asthma control test score achieved a median value of 24 points. : This study provides real-world evidence supporting the effectiveness of mepolizumab in managing CRSwNP in patients with features suggestive of type 2 inflammation. The observed improvements in patient-reported outcomes, nasal polyp burden, and asthma control suggest that mepolizumab may be a valuable therapeutic option for this patient population.