In 1937, Müller introduced the concept of a teratological sequence of thumb hypoplasia with increasing severity from mild deficiency, through severe deficiency, to thumb absence. Blauth subsequently detailed five specific grades. In 1992, Manske and McCarroll altered Blauth’s classification such that Grade 3 was sub-divided into Grades 3A and 3B, according to a presence or absence of the proximal metacarpal. Buck-Gramcko added a Grade 3C in which there was only a remnant metacarpal head. This article investigates their publications and those of others to identify ‘who said what’ and clarify the definitions of grades of thumb hypoplasia. A modification of Blauth’s classification is proposed, which retains the integrity of the concept of Müller and the skeletal and soft tissue grading of Blauth, but which also incorporates the disparate anomalies that may present in Grades 2 and 3 hypoplastic thumbs.