Introduction: We conducted a biomarker study to characterise exposure to pesticides among farmers and their families in Thailand to assess the relative importance of the dermal exposure route and to identify important factors that determine exposure levels within farmers' families. Methods: Sixteen farmers' families (eight vegetable and eight fruit farmers) participated in the study. Three morning spot urine samples were collected during a pesticide spraying week. Spot samples were grouped by individual and analysed for dialkylphosphate (DAP) metabolites and creatinine. Additional information on exposure and lifestyle was collected by means of questionnaires. Dermal exposure was assessed using a semi-quantitative observational method (DREAM). Results: Urinary DAP levels varied 20-fold between farmers, with average (geometric mean) levels of 51.1 μg/g for vegetable and 122.2 mg/g for fruit farmers. A moderate correlation (r s∼0.45) was found between loge-transformed DREAM scores and DAP levels. Farmers' urinary metabolite levels were not correlated with those of their spouses (r s∼-0.30) or children (r s∼-0.00) collected on the same days. Detectable spouses' DAP levels were on average (geometric mean) 13.0 mg/g and those of children 7.6 μg/g. Discussion: Farmers in Thailand as well as their families are exposed to pesticides in the spraying season and dermal exposure is an important route. The main route of exposure for farmers' families seems to be through transfer from the farmer to family members or contamination of the home environment, rather than family members helping or playing on the farm. Showering or washing immediately after pesticide spraying greatly reduces the potential exposure of family members to pesticide residues.