Malapropisms are lexical substitution errors resulting from a failure at the stage of accessing the phonological form corresponding to a lemma---a semantically and structurally specified lexical entry [Fay and Cutler (1977); Garrett (1980)]. An example is tentative for tenable. Since they occur naturally in utterance contexts, malapropisms are an important source of information about this stage of lexical access. A study of over 300 malapropisms confirmed prior findings that errors resemble targets closely in phonological form and in syntactic category. In addition, it was found that errors resemble targets in derivational morphology (independently of phonological similarity), and that there is a strong correlation (r[sup 2]=0.34) of the text frequencies of the error and target words. The partial correlations of frequency with word length, syntactic category, and segmental similarity only account for one-half of this correlation (residual r[sup 2] about 0.17). Models which treat frequency effects as biases on the decision processes of selecting word forms [Luce et al. (1990)] or as form activation thresholds [Jescheniak et al. (1994)] cannot account for such a correlation directly. The results thus appear to support some degree of organization of the lexicon according to frequency, as suggested, e.g., by Forster (1976).