An expanded protection motivation model was used to investigate the intention to give up smoking. Because smoking has both physiological and social-psychological foundations, the model was expanded to include the social dimensions as well as the original disease dimensions as predictors of health behavior. The participants were 96 current smokers (35 male and 61 female) in Australia; 44 were young adults (age < 22 years), and 52 were adults (age > 34 years). Data were analyzed by multiple regression with hierarchical entry, first of disease dimensions, then of social dimensions. For both the young and the adult smokers, the disease dimensions contributed significantly to the results of the regression equations. Addition of the social dimensions yielded a significant F change only for young smokers and increased the amount of variance explained from 23% to 38%.