Word frequency was determined for library books that primary-grade children selected for free reading. A survey of librarians determined which books these children selected. This list was reduced to 80 books through evaluations by elementary school teachers. A computer analysis of each word in these books revealed 105,280 running words. When proper names, onomatopoeic words, and easily recognizable inflected forms and compounds were omitted, there were only 3,220 different words in all of these books. A frequency count of these different words revealed that just 10 words account for almost one-fourth of all running words, 25 words account for over one-third of all running words, and 188 words account for almost seven out of 10 of all running words. It was suggested that systematic teaching of these high-frequency words would help insure that children have the background needed to read library materials of their own choosing at an early age. References and tables are given. (Author/DE)