I have never heard Sarah used as a nickname for Mary or Mary used as a nickname for Margaret and I have been doing research for over 20 years. I would say that if your family member is using Sarah instead of Mary, then that is not a nick name but one or the other is the first name and/or middle name. The following are what I know to be nicknames: Margaret (sometimes Americanized from Margaretta, Margaretha or Margarita) - Daisy,Greta,Madge,Maggie, Maisie, Marge,Margo,Meg,Megan,Metta,Midge, Peggie Mary - (sometimes Americanized from Maria) - Mae,Mamie,Maria(h),Marie, Marietta, Marion,Maureen, May, Mercy, Minnie,Mitzi, Mollie (y), Polly Sarah - Cera, Sadie,Sal,Sallie,Sara(i),Sukie, Surry Chyrl Lawrence-Bulger My Family Tree & All Its Branches _http://freepages.genealogy.rootsweb.com/~sodacat231/index.htm_ (http://freepages.genealogy.rootsweb.com/~sodacat231/index.htm)