Excess adipose tissue induces low‐intensity inflammation, which is an important pathogenetic factor adversely affecting the course of bronchial asthma (BA) in overweight/obese patients. The key effector cells of this inflammation are monocytes and macrophages. However, there are currently no studies characterising the effect of body mass index (BMI) on peripheral blood monocyte levels in children and adolescents with BA and their relationship with spirometric parameters reflecting bronchial patency. The aim of this study was to investigate the effect of BMI on peripheral blood monocyte and eosinophil levels and their relationship with spirometric parameters in children and adolescents with asthma.