Old Peculier (5.6% ABV) is Theakston's most famous beer. Old Peculier has been made under this name since the 1890s. In 2000, it won the silver medal in the Campaign for Real Ale (CAMRA)'s "Champion Winter Beer of Britain" 2000 competition. The label on the bottle describes it as a "full bodied, rich, smooth tasting ale with a mysterious and distinctive flavour". It is named after the peculier of Masham, a peculier being a parish outside the jurisdiction of a diocese.

