The significance of microalbuminuria (MA) in paediatric essential hypertension has yet to be established. The Leontio Lyceum ALbuminuria Study (3L Study) was designed to determine the prevalence of MA among Greek schoolchildren and to evaluate these rates in relation to the children's anthropometric and lifestyle characteristics, and dietary habits.During April 2009, 498 students from the Leontio Lyceum, aged 12-17 years (7th-12th grade), were asked to participate in the 3L Study. For each child a questionnaire was completed that was developed for the purposes of the study to retrieve information on socio-demographic and lifestyle characteristics, as well as dietary habits (through a semi-quantitative Food Frequency Questionnaire), and physical activity status. Overweight and obesity were defined using the international body mass index cut-off points established for children and young people. Office blood pressure (BP) was measured on two different occasions and those students who had BP >95th percentile for gender, age and height on both occasions were considered as hypertensives. Microalbuminuria was determined as albumin to creatinine ratio >or=22 mg/g in boys and >or=31 mg/g in girls in a morning spot urine sample using a quantitative assay (DCA 2000).The prevalence of MA was found to be 12.9% and that of childhood hypertension 5.2%. The prevalence of overweight status was 25.8% and 5.8% of the students were classified as obese. Low physical activity was reported by 7% of boys and girls, while 46.5% of the students reported participation in vigorous physical activities during a normal week. Based on the KIDMED score of each student, only 6% of them were classified as high adherers to a Mediterranean diet and 41.9% were classified as having very low diet quality.In this paper we present the aims, design and preliminary results of an epidemiological study on MA, hypertension, increased body size and lifestyle characteristics among Greek schoolchildren.