Purpose: Cysteinyl leukotrienes (CysLTs) have been recognized as key mediators associated with type 2 inflammation in the airways of asthmatic patients. CysLTs are associated with airway constriction, eosinophil recruitment/activation, and airway remodeling. The study aimed to understand the role of CysLTs in adult asthmatics in a real-world clinical setting. Methods: One hundred five adult asthmatics who had maintained antiasthmatic medications were enrolled. Asthmatic subjects were classified into 2 groups according to urinary leukotriene E4 (uLTE4) levels, and their clinical parameters and inflammatory mediators, including forced expiratory volume in 1 second (FEV1) %, fractional exhaled nitric oxide (FeNO), blood eosinophil count, serum periostin (sPON), and urinary eosinophil derived neurotoxin (uEDN) were compared between the high-uLTE4 and low-uLTE4 groups. Results: The prevalence of chronic rhinosinusitis (CRS), severe asthma, and aspirin-exacerbated respiratory disease (AERD) were significantly higher in the high-uLTE4 group than in the low-uLTE4 group. The high-uLTE4 group had lower FEV1% and maximal midexpiratory flow %, but higher FeNO levels than the low-uLTE4 group. In addition, blood eosinophil count, sPON, and uEDN levels were significantly higher in the high-uLTE4 group than in the low-uLTE4 group. The presence of AERD and levels of FeNO, sPON, and uEDN were significantly associated with higher uLTE4 levels in asthmatics. Conclusion CysLTs are associated with type 2 inflammation in the airways of asthmatic patients, contributing to the development of AERD, CRS, and asthma severity. The stratification of clinical phenotypes according to the uLTE4 level could support optimizing anti-inflammatory therapy for better control of asthma.