ABSTRACT: Telephone-based tobacco quitlines are an evidence-based intervention, but little is known about how callers hear about quitlines and whether variations exist by demographics or state. This study assessed trends in "how-heard-abouts" (HHAs) in 38 states.Data came from the Centers for Disease Control and Prevention's (CDC's) National Quitline Data Warehouse, which stores nonidentifiable data collected from individual callers at quitline registration and reported quarterly by states. Callers were asked how they heard about the quitline; responses were grouped into the following categories: media, health professional, family or friends, and "other." We examined trends from 2010 through 2013 (N = 1,564,437) using multivariable models that controlled for seasonality and the impact of CDC's national tobacco education campaign, Tips From Former Smokers (Tips). Using data from 2013 only, we assessed HHAs variation by demographics (sex, age, race/ethnicity, education) and state in a 38-state sample (n = 378,935 callers).From 2010 through 2013, the proportion of HHAs through media increased; however, this increase was not significant when we controlled for calendar quarters in which Tips aired. The proportion of HHAs through health professionals increased, whereas those through family or friends decreased. In 2013, HHAs occurred as follows: media, 45.1%; health professionals, 27.5%, family or friends, 17.0%, and other, 10.4%. Media was the predominant HHA among quitline callers of all demographic groups, followed by health professionals (except among people aged 18-24 years). Large variations in source of HHAs were observed by state.Most quitline callers in the 38-state sample heard about quitlines through the media or health care professionals. Variations in source of HHAs exist across states; implementation of best-practice quitline promotional strategies is critical to maximize reach.