The Impostor Phenomenon (IP) was investigated with respect to both its personal and situational aspects. Situational predictors included self-perceived uniqueness and environmental ambiguity. The role of organizational socialization as a moderator of the IP at organizational entry was also investigated. A repeated measures design, which included two measurement phases and which spanned the course of 4 months, also permitted the investigation of the stability of the construct over time. A sample of 154 male and female volunteers, at the commencement of their graduate studies, completed two sets of questionnaires, one at the beginning of the academic year and the second after completion of the first semester. The Clance Imposter Scale (Clance, 1985), the Rosenberg Self-Esteem Scale (Rosenberg, 1965), and a modified version of the Imes' Attribution Questionnaire (Imes, 1979) were included at both phases of data collection. In addition, the first survey included the Measure of Self-perceived Atypicality (Harvey, 1981), while a subset of the Role Conflict and Ambiguity Questionnaire (Rizzo, House & Lirtzman, 1970) and two original measures of organizational socialization were included in the second survey. Demographic characteristics, including gender, age, ethnicity, degree type, university department, and socioeconomic status (SES), were also collected. (Abstract shortened by UMI.)