The purpose of this study was to examine the extent to which loneliness mediates the relationship between perceived social support and positive health practices of young adults, ages 22 to 34, by testing a mediational model of relationships in a three-variable system developed through theory and previous research. Data were collected from 70 young adults who were attending classes in a large urban university. They responded to the PRQ85-Part II, the Revised UCLA Loneliness Scale, the Lifestyle Questionnaire, and a demographic data sheet. Statistically significant correlations were found between perceived social support and positive health practices, perceived social support and loneliness, and loneliness and positive health practices. A series of regression analyses designed to test for mediation were performed. The results indicated that loneliness is a dominant mediator in the relationship between perceived social support and positive health practice. Implications for practices are discussed.