Quantitative information about historical changes in natural ecosystems is important for guiding management interventions. However, few accurate data sources are available for documenting long-term vegetation changes. In this paper, we describe a neglected source of quantitative information on historical forest structure: forest inventory strip surveys, which were widely used in eastern Australia from 1915 to the 1940s. Strip surveys provide quantitative information on the species composition, stem density, basal area, stem form and size class distributions of dominant tree species. Such information is not available from other widespread data sources. Strip surveys usually surveyed 10% of the total forest area. In this paper, we describe the original survey methods, demonstrate how to decode data-book entries, and analyse a sample dataset from the Pilliga State Forests in northern New South Wales to illustrate the information that can be obtained from this material. Strip survey data-books are poorly archived. Many books exist for Eucalyptus–Callitris forests in northern and central NSW, and additional books may exist for many other forest types in eastern Australia. Strip surveys provide a valuable data source for studying long-term vegetation changes in forest ecosystems. We urge forest managers to search for and preserve this precious archival material.