The Scottish Public Services Ombudsman (SPSO), Jim Martin criticised Hairmyres Hospital in East Kilbride for failing to properly care for the man, who had dementia.
He upheld a complaint against the hospital and found that there were "unreasonable failings" in relation to the medical and nursing care and treatment in relation to pneumonia and medication.
The 72-year-old patient, known only as Mr C, had Alzheimer's and chronic obstructive pulmonary disease when he was admitted to the Lanarkshire hospital on March 10, 2010. His wife, Mrs C, complained to NHS Lanarkshire that, on some occasions, she found his dementia medication among his sheets and on the floor of the ward.
She also reported that his room window was open and he had no blankets on his bed, leaving him "very cold".
Jim Martin's report adds Mrs C also felt "Mr C was not being appropriately supervised at meals, resulting in malnourishment."
Mr C discharged himself against advice on March 23, 2010. He was cared for at home but died on April 2.
Mr Martin's report reads: "She was deeply concerned that his dementia was not appropriately recognised or managed by staff at the hospital." Staff noted Mr C was "wandering in the ward", which Mrs C said showed they didn't recognise his dementia adequately.
On March 22, he tested positive for the superbug MRSA. Staff also noted that Mr C was thin but no record was kept of his weight.
In his conclusion, Mr Martin said: "Mrs C's concerns about the care were so great, and she was given no reassurance, to the point that she decided Mr C would be better cared for at home. This lack of confidence in the standard of care should not have been allowed to develop in the first place."
He recommended that NHS Lanarkshire ensure compliance with medicine management and provide evidence on the implementation of the Scottish National Dementia Strategy.
An NHS Lanarkshire spokesman said it had "fully accepted the recommendations".