Objectives Asthma treatment guidelines recommend inhaled corticosteroids (ICS) as the first-line therapy. However, ICS are prescribed to lower percentages of asthmatic patients in Japan than in other developed countries. The aim of this study was to reveal factors affecting the prescription of ICS for asthmatic adults. Methods Using insurance claims data in Kyoto Prefecture, Japan, we performed a cross-sectional study. We assessed whether outpatients aged 15 years or older who were diagnosed with asthma had received ICS or not, and conducted logistic regression analyses to identify patients' and facilities' factors associated with ICS use. Results We analysed 13428 asthmatic adults, of which 51% were prescribed ICS. Patients receiving asthma care at facilities with respiratory or allergy specialists were more likely to receive ICS than facilities without specialists (adjusted odds ratio 2.70; 95% confidence interval 2.462.97). Those aged 75 years or older were less likely to receive ICS than those aged 15 to 64 (adjusted odds ratio 0.71; 95% confidence interval 0.640.78). An examination of the interaction between the presence or absence of specialists and facility training status suggested that whether asthmatic adults received ICS depended on the former factor rather than the latter. Conclusion The presence of specialists in facilities and the age of patients were strong factors affecting ICS prescription. Increases in ICS therapy for the elderly and ICS prescription by non-specialists would lead to an overall increase in patients receiving ICS and consequently achieving the goal of asthma control.