Purpose. To determine the percentage of parents who report quitting spontaneously and examine the factors associated with these quits. Methods. As part of a cluster randomized control trial addressing parental smoking in a pediatric outpatient setting, 12-month follow-up survey data were collected from parents who had self-identified as smokers when exiting from 10 control practices. Parents were considered to have made a spontaneous quit if they reported not smoking a cigarette, even a puff, in the last 7 days and chose the statement “I did not plan the quit in advance; I just did it” when describing how their quit attempt started. Results. Of the 981 smoking parents enrolled at baseline, 710 (72%) completed the 12-month follow-up. Of these, 123 (17%) reported quitting, of whom 50 (41%) reported quitting spontaneously. In multivariable analysis, parents who reported smoking on some days vs. every day (OR 3.06 (95% CI 1.42, 6.62)) and that nobody had smoked in their home/car vs. someone had smoked in these settings in the past 3 months (OR 2.19 (95% CI 1.06, 4.54)) were more likely to quit spontaneously. Conclusions. This study shows that, of parents who quit smoking, a substantial percentage report quitting spontaneously and that intermittent smoking and smoke-free home/car policies are associated with reports of quitting spontaneously. Promoting smoke-free home/car policies, especially when parents are not willing to make a plan to quit smoking, might increase the likelihood that parents decide to quit without advance planning. Pediatric healthcare providers are uniquely positioned to use the child’s visit to motivate parents to quit smoking and eliminate their child’s exposure to tobacco smoke, regardless of the frequency of smoking or a readiness to plan a quit attempt. Clinical Trial Registration. This trial is registered with NCT01882348.