It is known that the prevalence of gastroesophageal reflux disease (GERD) in asthmatic patients is high. Although an endoscopic diagnosis of GERD based on the established Los Angeles (LA) classification requires the detection of erosive mucosal breaks, there are patients with GERD who have prominent erythema of the esophageal membrane without erosive mucosal breaks. Non-erosive mucosal change denotes the minimal change of the discoloring type of reflux esophagitis. This study was undertaken to determine the prevalence of GERD in asthmatic patients using the LA classification with the inclusion of minimal change, compared to the prevalence determined using the established LA classification without minimal change. The presence of GERD in asthmatic patients (n = 78), non-asthmatic disease control patients (n = 56), and healthy subjects (n = 150) was evaluated by endoscopic examination. The frequency of GERD in asthmatic patients based on the LA classification with minimal change was higher (54/78, 69.2%) than in asthmatic patients based on the LA classification without minimal change (37/78, 47.4%) (p < 0.05). The prevalence of GERD in asthmatic patients (69.2%) was higher than that in disease control patients (17/56, 30.4%) and healthy subjects (27/150, 18.0%) based on the LA classification with minimum change. These data indicate that asthmatic patients have a high frequency of GERD. In addition, without the inclusion of minimum change to the diagnosis of GERD, the prevalence of GERD appears to be underestimated in asthmatic patients. Therefore, physicians should carefully observe asthmatic patients with minimal change on endoscopy.