BACKGROUND: Environmental tobacco smoke (ETS) is an important risk factor. The aim of this study is to evaluate effects of the counseling method "Smoke-free children" that focuses on protection of infants. METHODS: The counseling method, "Smoke-free children", has been developed and implemented at Swedish child health centers. The counseling method's point of departure is based upon a client-centered approach. Saliva cotinine samples from the mothers were collected when the child was 1-4 weeks and 3 months of age. Interviews regarding mothers' smoking habits and self-reported maternal smoking were also carried out. RESULTS: Forty-one mothers participated in the study, 26 in the intervention group and 15 in the control group. Cotinine was collected from 22 subjects in the intervention and 8 in the control group. Before the intervention, the mean cotinine level was 185 ng/mL in the intervention group and 245 ng/mL in the control group. After the intervention, cotinine levels were reduced in the intervention group (165 ng/mL) and increased in the control group (346 ng/mL). Yet, after the intervention, the mothers themselves reported more smoking in the intervention group than in the control group. Only weak correlations were found between self-reported smoking and cotinine. CONCLUSIONS: The statistical analysis supports the view that a client-centered intervention, aimed at increasing self-efficacy, exerts a positive effect on maternal smoking in the prevention of infant exposure to ETS, when applied in a routine clinical setting.