Loneliness is a psychological construct that has been reported in a variety of populations and associated with a number of other negative psychological problems. This study was an examination of coefficient alpha of a prominent measure of loneliness: the University of California, Los Angeles (UCLA) Loneliness Scale (Russell, Peplau, & Cutrona, 1980; Russell, 1996). We utilized reliability generalization to provide an aggregate estimate of the reliability of the scale over time and in a variety of populations as well as to assess and identify sampling and demographic characteristics associated with variability in coefficient alpha. Of the 213 studies examined, 80 had reported alpha estimates, and we used them in this analysis. We discuss conditions associated with variability in coefficient alpha along with pertinent implications for practice and future research.