Previous research has shown that objective measures of orthographic (i.e., spelling) similarity can predict the probability of drug-name confusion, but it is not clear how these objective measures relate to subjective judgments of similarity. This study examined the association between one objective measure of orthographic similarity, the Dice coefficient on trigrams, and one subjective measure, based on the Proscale multidimensional scaling system. Twenty-seven participants, divided into three groups, performed a similarity grouping task on one of three sets of 70 drug names drawn at random from a larger set of similar and dissimilar name pairs. Subjective groupings were converted to dissimilarity scores with the use of the Proscale multidimensional scaling program. The association between subjective and objective measures was assessed by correlation and regression analyses. Correlations between subjective and objective measures were −0.70, −0.48, and −0.53 for the three groups, respectively (p < .001). Regression models with trigram similarity as the main predictor accounted for between 22 and 48% of the variance in subjective dissimilarity scores. It is concluded that objective measures of orthographic similarity between drug names are valid but incomplete measures of subjective similarity. © 2002 Wiley Periodicals, Inc.