The role of hypervalent iodine reagents as oxidants has been widely recognized for more than 20 years. As electrophilic species, they could also play the role of Lewis acids. While not surprising, this aspect of these reagents has not been fully considered and exploited in the literature. The experimental quantification of the Lewis acidity of a small series of diaryliodonium salts was performed using the Gutmann-Beckett method. Validation of a theoretical model using the experimental data was done in order to predict the Lewis acidity of other cationic iodine(III) species. Comparison with known common Lewis acids is presented.