This paper reports on preschool children's social relationships developed in urban and rural kindergarten classes in Greece. We investigated the selection and rejection criteria children use and examined potential criteria differences as a function of a number of socio-demographic variables (children's age group, gender, parental job status, region of kindergartens' base). The sample consisted of 70 children (30 boys and 40 girls), 4-6 years old, from one urban- and one rural-based kindergarten. The findings of the study indicated that: (1) the children used two criteria on average; (2) as they grow up, children's choices and explanations present a quantitative increase; (3) rejections are attributed to the level of their classmates' negative behaviour, mainly their aggressiveness; and (4) children's explanations for their positive selections seem to focus on their 'common interests/play', 'closeness/kinship' and 'personality characteristics'. These findings are discussed in relation to the study's hypotheses, which they support in part.