The first study in this paper examined the hypothesis that feeling lonely is related to a self-perceived lack of self-disclosure to significant others. Thirty-seven male and 38 female undergraduates rated themselves on the UCLA Loneliness Scale and the Jourard Self-Disclosure Questionnaire. Analyses showed that for males and females, loneliness was significantly and linearly related to a self-perceived lack of intimate disclosure to opposite-sex friends. For females, loneliness was also associated with a perceived lack of self-disclosure to same-sex friends. The second study investigated the relationship between loneliness and actual disclosure behavior. Twenty-four lonely subjects and 23 nonlonely subjects were paired with nonlonely partners in a structured acquaintanceship exercise. Both opposite-sex pairs and same-sex pairs were included in the design. Postexercise ratings by partners indicated that lonely subjects were less effective than nonlonely subjects in making themselves known. Analysis of the intimacy level in the conversations showed that lonely subjects had significantly different patterns of disclosure than nonlonely subjects. We suggest that the self-disclosure style of the lonely person impairs the normal development of social relationships.