Retention of aging ewes is a strategy producers may use to maintain or increase flock size. Older ewes can have a higher risk of mortality and health issues, but these may be minimised with early intervention and culling. This retrospective study examined the incidence and causes of mortality and culling in a flock of Merino ewes as they aged from 4.5 to 5.5 until 9.5 to 10.5 years. The annual rate of ewe mortality ranged from 6.2% to 9.9%, with lambing complications being the major source of reported loss. Annual culling rates ranged from 1.6% to 42.8%, the larger rates reflecting opportunistic replacement with younger ewes rather than essential culling to maintain welfare and productivity. The major reasons for culling were low condition score, worn or missing teeth or faulty udders. The incidence of other faults was low. Only 18.3% of ewes remained when aged 9.5–10.5 years and these were fertile (89% pregnant) with a high proportion of multiple fetuses (52%) in their final year, although fleece weight had declined. Younger ewes born in 2004/2005 tended to have lower annual mortality rates than the aged ewes, but 8%–12% were still culled annually. It is concluded that an annual inspection pre-joining of all ewes and preventative culling for health issues is necessary to minimise any increase in mortality and risk to ewe welfare from retaining aging ewes. More frequent inspection will be required as potential health issues develop during the year, as these may not be evident pre-joining.