Aims To test the effectiveness of tailored quitline (telephone) counselling among smoking parents recruited into cessation support through their children's primary schools. Design Two-arm randomized controlled trial with 3- and 12-month follow-up. Setting Proactive telephone counselling was administered by the Dutch national quitline. Participants Smoking parents were recruited through their children's primary schools and received either intensive quitline support in combination with tailored supplementary materials (n = 256) or a standard self-help brochure (n = 256). Measurements The primary outcome was 7-day point-prevalence abstinence at 12-month follow-up. Also measured were baseline characteristics, use of and adherence to nicotine replacement therapy and pharmacotherapy, smoking characteristics and implementation of a home smoking ban. Findings Parents who received quitline counselling were more likely to report 7-day point-prevalence abstinence at 12-month assessment [34.0 versus 18.0%, odds ratio (OR) = 2.35, confidence interval (CI) = 1.56-3.54] than those who received a standard self-help brochure. Parents who received quitline counselling were more likely to use nicotine replacement therapy (P