The paper discusses the variation of a surname that currently sounds like Dianov over the history of one family. Different variants were retrieved from the official documents preserved in the family archive and from the State Archive of the Sverdlovsk Region, as well as from private correspondence of the 18th–20th centuries, which helped restore the chronology of changes. The authors suggest their own hypothesis about the original form of the surname and the deriving personal name, as well as about the etymon of the latter. In parallel, they also consider the etymologies of the surname Dianov available in literature. The analyzed surname is distinguished from the surname Dianov which, as the authors believe, has clerical origin tracing to the name of the ancient goddess Diana. The deformation of the surname over the course of two centuries could be caused by both objective linguistic factors (the extinction of the sound denoted in Cyrillic by the letter yat, and then the letter itself, the interchange of the letters e/i due to the reduction of unstressed vowels, the loss of etymology of the surname, etc.), as well as subjective factors (insufficient qualifications of employees of civil registration departments, negligence in the preparation of documents, illegible handwriting, etc.). The paper also provides statistics of the existing variants of the surname at the present time (according to the Internet), as well as settlement and street names in Russia derived from it. The surname Deyanin / Diyanin receives a new interpretation in the light of the considered phonetic processes. The conclusion is made about the possibility of an independent development of similar surnames with different origin.