Data concerning safety of treatment in schoolchildren cannot be extrapolated to preschool children due to differences in growth velocity and metabolism. The safety issue in preschool children is further complicated by insufficient knowledge of the optimal dose, and the lung delivery from the devices available. Systemic activity has often been studied as a marker of adverse clinical effect. However, with improving technology, systemic activity can be detected within the range of the normal biological feedback system, where it is of no clinical importance. Therefore, systemic activity is not synonymous with clinically relevant side-effects. Side-effects should be assessed in specific clinical studies. Effect on growth velocity is a potential side-effect of major interest. Knemometry is a sensitive measure of short-term growth of the lower leg length in schoolchildren as well as in preschool children, which enables precise measurements of systemic activity, but it is not a measure of statural growth. The only clinically relevant outcome measure of human growth is the final height in relation to expected final height, allowing for gender and midparental height differences. In addition to effects on statural height, osteoperosis is an important potential side-effect. The importance of bone density during preschool age for final adult bone mineral density needs to be studied. Cataract formation is a side-effect associated with systemic steroid treatment and may be of special consideration during treatment with nebulized steroids, which may expose the eyes to high doses. Thrush, dysphonia and local skin atrophy in steroid-exposed areas are potential local side-effects, and yet the incidence in young children is unknown and dependent on the device used for delivery. When considering adverse effects of treatment, the risk of side-effects from undertreatment should always be observed.