Prior research indicates that category labels influence category judgments, but little is known regarding the effects for familiar categories with significant social consequences. The present studies address this issue by examining the effect of linguistic form on judgments of illnesses. Both mental and physical illnesses were presented in each of three linguistic forms: noun, adjective, and possessive phrase. In Study 1, participants were asked to judge the permanence of a set of novel illnesses that differed in wording (e.g., "He is a baxtermic"; "He is baxtermic"; "He has baxtermia"). In Studies 2 and 3, participants were asked to judge which forms of wording were most familiar for actual mental illnesses (e.g., schizophrenia) and physical illnesses (e.g., diabetes). In Study 4, participants were asked to judge the permanence of a set of familiar illnesses that differed in wording. The results indicated that for "novel" illnesses, nouns ("is a") imply greatest permanence and possessive nouns ("has") imply least permanence. However, for "familiar" illnesses, permanence judgments are also influenced by how frequently each form appears in ordinary language use. Mental illnesses are more often expressed with relatively permanent forms ("is" and "is a") , whereas physical illnesses are more often expressed with relatively transient forms ("has"). The results demonstrate the importance of both linguistic form and conventional wording patterns on how categories are interpreted.