A Blenheim man was today cleared of having sex with his adult daughter.

The man was today found not guilty in Blenheim District Court of five charges of sexually assaulting his daughter, the Marlborough Express reported.

The charges followed an incident in August last year when the daughter, then aged 31, went to her parents' home after her mother was admitted to hospital with a possibly terminal illness.

The daughter drank alcohol with family members, then in the early hours of the morning her father invited her and her young son to sleep in a bed with him.

Defence lawyer Rob Harrison said the daughter's inebriation and the accused's trauma and lack of sleep from looking after his wife, resulted in the usual barriers breaking down between father and daughter.

"It was inappropriate and it was wrong but it was not rape."

He said the daughter did not "come to bed intending to have sex with her father".

"No one is saying she did...they weren't thinking of where they were, or who they were...it just happened."

The woman complained to Women's Refuge the next morning.

The man has permanent name suppression.