Her agent Phil Belfield said O'Mara died Sunday in a nursing home in southern England after a short illness.
The actress, who began her television career in the 1960s, became a household name for playing Alexis Colby's scheming sister Cassandra "Caress" Morrell in "Dynasty." She also appeared in the original run of British series "Doctor Who" and BBC drama "Howards' Way."
In the 1990s she starred in the comedy show "Absolutely Fabulous" with Joanna Lumley.
