Background: Interventions to help parents quit smoking may yield important benefits for children with asthma. Children’s exposure to environmental tobacco smoke can be measured by reporting of an adult in the household and testing the child’s biomarker, e.g., cotinine. Objective: The aim of the study was to assess the effectiveness of “face-to-face” intervention carried out since 2016 in families with children diagnosed with asthma 3 years after beginning the anti-tobacco intervention. Methods: This study was a follow-up to an interventional study that assessed the effectiveness of direct patient education versus educational leaflets alone about parental tobacco smoking. The patients with asthma (ages 4‐17 years) enrolled in our original intervention study conducted in 2016 were under the care of the allergy outpatient clinic. The active group was individually educated about the harmful effects of environmental tobacco smoke on their children. The control group included patients and parents, among whom only leaflets were distributed. After 3 years of ongoing intervention, in patients from both groups, exposure to tobacco smoking was evaluated with a questionnaire addressed to parents and/or caregivers and measurement of cotinine in children’s urine. The forced expiratory volume in the first second of expiration and fractional exhaled nitric oxide levels were measured. Results: Seventy participants completed the study: 37 in the active group and 33 in the control group. In the active group, 27% of the parents quit smoking entirely compared with 9.4% of parents in the control group. In the group of active intervention, a significant decrease in the cotinine level (p < 0 .001) and the number of cigarettes smoked daily were observed (p < 0.001) 3 years after the active intervention compared with values right after the intervention. In the control group, there were no significant changes in the above-mentioned parameters. Conclusion: “Face-to-face” intervention among families with smokers were effective and lowered cotinine levels in children with asthma and the number of cigarettes smoked assessed 3 years after the intervention.