Lily Hartley was in Bradford Royal Infirmary when two rings, which had belonged to her late husband, were taken.
Her granddaughter, Emma Hartley, reported the theft on Facebook and said the rings had sentimental value.
Bradford Teaching Hospitals NHS Foundation Trust said it "sincerely apologised" to the family.
A spokesperson added they were "fully investigating the matter."
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West Yorkshire Police said it had been alerted to the theft relating to Mrs Hartley and also a second one at the hospital.
Officers said it believed two victims, both women in their 80s, had items of jewellery taken between the 26 and 29 March.
Hospital bosses have apologised after a woman in her 80s had jewellery stolen whilst in hospital.