The aim of this randomized-controlled trial was to evaluate the effectiveness of an intensive intervention to reduce children's environmental tobacco smoke (ETS) exposure at their home compared with a minimal intervention. The target population of the study was the mothers of children aged 1-5 who lived in the Cengizhan district of Izmir in Turkey, who smoked and/or whose spouses smoked. It was found that at least one parent of a total of 182 children smoked and 80 of these mothers were taken into stratified sampling based on the number of the smoking parents. Mothers were visited at their homes. During the initial visit, they were educated and urine samples were taken from their children. Following this initial visit, mothers were randomized to the intensive intervention (n = 38) or the minimal intervention group (n = 40). The levels of cotinine in the intensive intervention (P = 0.000) and minimal intervention (P = 0.000) groups in the final follow-up were significantly lower than the initial levels. The proportion of mothers reporting a complete smoking ban at home in the final follow-up was higher in the intensive intervention group than the minimal intervention group (P = 0.000). The education provided during the home visits and the reporting of the urinary cotinine levels of the children were effective in lowering the children's exposure to ETS at their home.