Representation of disability in school textbooks may influence pupils' knowledge and perceptions of people with disabilities. The aim of this study was to investigate representation of people with disabilities in school textbooks. The study employed a mixed-methods approach. Quantitative frequency analysis was used to investigate the extent of representation of disabilities in texts and pictures in 78 Norwegian textbooks for Grades 5-10. Regarding texts, the results showed that people with disabilities were represented in less than half of these textbooks (49%). Concerning pictures, people with disabilities were even less represented, appearing in only 29% of the textbooks. These quantitative findings were supplemented by a qualitative survey of textbook authors, who were asked to explain the marked absence of disability references in their own books and in school textbooks in general. The two most frequent explanations were that textbook authors had either overlooked people with disabilities, or that the Norwegian National Curriculum (Kunnskapsdepartementet 2006. "Laererplanverket for Kunnskapsløftet" (LK06) [The Norwegian National Curriculum]. https://www.udir.no/lk20/overordnet-del/) did not explicitly mention this minority. We discuss these explanations as expressions of conscious considerations rather than unconscious omissions.