This study examined selection bias by comparing characteristics of a general population sample of tobacco chewers, participants in a chewing tobacco cessation trial, and non-participants in the trial. A population-based sample of chewers (n = 155) was surveyed by telephone to assess demographics, tobacco-use patterns, and quitting history. Six months later, chewers from this same population were recruited for a cessation trial (n = 401 participants and 68 non-participants). Trial participants differed little from general population chewers on demographics, but they used more chew and were more dependent on nicotine. They were more likely to have tried to quit, received advice to quit and experienced tobacco-related health problems. Trial non-participants were virtually identical to participants on demographic and tobacco use measures. The findings suggest that clinically tested treatments are generalizable beyond the research setting, because trial participants are demographically representative of the general population of chewing tobacco users, are not biased toward light users, and are representative of those chewers most likely to seek out community-based cessation services outside the trial context.