BACKGROUND Corticosteroid cross-reactions have been classified into four well-defined groups. A previous study of patch test reactions to other corticosteroids in patients allergic to hydrocortisone failed to conform to these groups. It was suggested that substitution at the C6 and C9 positions of the corticosteroid was the most important determinant of a further reaction. OBJECTIVE Our aim was to analyze multiple positive patch tests to corticosteroids in patients sensitized to budesonide to confirm our earlier findings. METHODS Forty-six patients with positive patch tests to budesonide were patch-tested to 17 other topical corticosteroids. The results were examined by a generalized linear model and a chi-square test. RESULTS Substitution of the corticosteroid at the C6 and C9 positions significantly reduced the number of reactions. A different substitution at the C16 and C17 positions was less important, and that at the C21 position was of no significance. CONCLUSIONS Patients sensitized to budesonide are most likely to react to other non-C6 and non-C9 substituted corticosteroids.