Based on the previously established personality correlates of frequent lucid dreaming and frequent nightmare dreaming, several hypotheses were generated regarding the boundary characteristics of these dreamers relative to each other and to a control group of non-lucid and comparatively nightmare-free dreamers. The data from Hartmann's Boundary Questionnaire obtained from 40 subjects in each dreamer group (who were individually matched for sex, age, and background as far as possible) were analyzed. The results of the study give evidence that lucid dreamers have "thin" boundaries in many of the same senses that nightmare sufferers do, but can be differentiated from nightmare dreamers by the greater degree of coherence of their psychological sense of self as measured on the Self-Coherence Subscale of the Boundary Questionnaire. The suggestion is made that, given the similarity of "thin" boundaries, perhaps nightmare sufferers could become lucid dreamers and possibly resolve their nightmare condition while in the dream state.