The purpose of this study was to explore how parents and their young children attended to mathematical concepts as they engaged in shared book reading. Thirty-nine parents and their 4-year-old children from a culturally diverse metropolitan area were videotaped as they read "Mr. McMouse" (Lionni, 1992) and "Swimmy" (Lionni, 1963). Shared reading episodes were transcribed in their entirety and the data were coded according to a scheme developed by the authors (Anderson, Anderson, & Shapiro, 2004). All families except one engaged in mathematical talk although there was considerable diversity in terms of the amount of talk and the ways in which mathematical concepts were shared. The concept of size arose most frequently, next was different aspects of number, while shape occurred relatively infrequently. Results suggest that shared book reading holds considerable potential for parents to draw attention to mathematical vocabulary and concepts. (Contains 1 table and 2 appendices.)