The demographics of households with a cell phone and no landline differ significantly from landline households; cell-only households are more likely to be younger, rent their home, and live alone or with unrelated roommates. There is growing concern that landline-based random digit dial (RDD) survey research that excludes cell-only households is resulting in undercoverage of the population, threatening the generalizability – and therefore the utility – of RDD surveys, such as the Behavioral Risk Factor Surveillance Survey (BRFSS). The population currently living as cell-only is projected to surpass 25% by the end of 2008; including this population in telephone survey research is vital to ensuring accurate health estimates. To advance our understanding of the implications of the growing cell-only population on health research, we conducted a randomly selected nationwide survey of cell-phone users. This survey included both cell-only respondents and respondents who completed the survey via cell phone but who also have a landline. In previous research, we’ve found that there are significant health differences between cell-only adults and those who maintain a landline, but many of these differences are mitigated with demographic weighting. As the cell-only population grows, we hypothesize that these disparities will have a greater impact on accuracy–thus, relying on weighting adjustments to account for the cell-only population will become an unknown risk. Therefore, we continue to monitor the assumption that demographically adjusted RDD estimates are accurately representing the adult population. Further, we compare health characteristics of cell-only respondents to data for adults living in cell-only households as measured by the National Health Interview Survey (NHIS). Similarly, we compare cell users who still maintain a landline to NHIS adults living in households with both a landline and a cell phone. These comparisons assess the ability to accurately measure cell phone users via cell phone interview.